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Notes  on  the  Geology 

IN  THE 

Vicinity  of  Bennington,  Vt. 


G.  E.  Gordon 


UHW.  Of  KlliSS.  ffiW^ 


From  the  Ninth  Report,  Vermont  State  Geologist,  1914. 


Notes  on  the  Geology 

IN  THE 

Vicinity  of  Bennington,  Vt. 


G.  E.  Gordon 


LO 

CO 

■• —  From  the  Ninth  Report,  Vermont  State  Geologist,  1914. 


LEGEND 


NOTES  ON  THE  GEOLOGY  IN  THE  VICINITY  OF 
BENNINGTON,  VERMONT. 


C.  E.  Gordon. 


TABLE  OF  CONTENTS. 

Introduction. 

Location. 

Topography. 

Drainage. 

General  Geology. 

General  Relations  of  Geology  and  Topography. 

Table  of  Rock  Formations  and  Component  Members. 

The  Gneiss  and  Associated  Quartzite. 

The  Valley  Quartzite  South  of  Bennington. 

The  Valley  Quartzite  and  Interbedded  Limestones  and  Quartzite  North 

of  Bennington. 
The  Limestone  Formation  in  and  South  of  Bennington. 
Limestone  and  Schist  Northwest  of  Bennington. 
Limestone  and  Schist  of  Mt.  Anthony. 

The  Limestone  and  Schist  in  North  Pownal  and  Pownal  Villages. 
The  Schist  of  Mann  Hill. 
The  Schist  and  Limestone  of  Mason  Hill. 
General  Relations. 
The  Pleistocene. 

INTRODUCTION. 

In  the  summer  of  1912  the  writer  spent  two  and  one-half 
weeks  in  the  study  of  the  geology  in  the  vicinity  of  Bennington, 
Vt.  Though  the  work  speedily  involved  a  detailed  inspection 
from  outcrop  to  outcrop,  it  was  purposely  carried  out  as  a  recon- 
naissance. It  was  expected  that  another  season's  work  would 
bring  out  the  broader  structural  relations  among  the  different 
formations  and  lead  to  more  positive  conclusions  with  which  to 
return  to  the  task  of  mapping  the  Bennington  region. 

It  has  proved  inadvisable  to  carry  out  the  original  plan.  In 
view  of  the  brief  period  spent  in  the  field  and  the  intricate  nature 
of  the  problem  only  such  notes  as  were  collected  and  such  sugges- 
tions as  they  seem  to  afford  can  be  offered  in  this  report. 

Attention  was  chiefly  given  to  the  hard  rock  formations.  So 
far  as  observed,  the  surface  deposits  offer  no  special  features 
of  interest. 


338  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

A  map  is  offered  herewith  to  show  the  outcrops  which  were 
examined.  The  boundaries  of  the  different  formations  are  drawn 
in  on  the  basis  of  these  observations.  Certain  probable  structural 
relations  are  involved  which  are  also  exhibited  on  the  map  and 
discussed  in  the  report. 

LOCATION. 

The  area  discussed  in  this  paper  is  situated  in  the  extreme 
southwestern  part  of  Vermont  and  forms  approximately  the 
western  third  of  the  Bennington  quadrangle.  The  southern 
boundary  of  the  Bennington  sheet  is  on  the  west  less  than  one- 
half  a  mile,  and  on  the  east  somewhat  more  than  a  mile  from  the 
Massachusetts  line.  The  western  part  of  the  map  includes  a  strip 
of  the  Hoosick  quadrangle,  varying  in  width  from  a  mile  and  a 
half  to  two  miles,  which  separates  the  western  margin  of  the 
Bennington  sheet  frorh  the  New  York  State  boundary. 

The  Bennington  quadrangle  lies  between  parallels  42°  45' 
and  43°  north  latitude  and  meridians  7Z°  and  72)°  30'  west 
longitude.  The  particular  parts  of  the  quadrangles  discussed  in 
this  paper  embrace  the  townships  of  Pownal  and  Bennington, 
the  major  part  of  Shaftsbury  and  small  strips  on  the  west  of 
Stamford,  Woodford  and  Glastenbury. 

TOPOGRAPHY. 

The  area  includes  the  southern  portion  of  the  great  limestone 
"valley  of  Vermont."  Within  the  Bennington  quadrangle  the 
valley  is  hemmed  in  on  the  east  by  the  steep  western  slope  of  the 
Green  Mountain  Plateau,  which  extends  as  a  rugged  wilderness 
through  the  towns  of  Stamford,  Woodford  and  Glastenbury. 
East  of  Bennington  the  plateau  is  cut  by  the  northeast-southwest 
valley  of  Walloomsac  Brook.  North  of  this  stream  are  the  espe- 
cially rugged  masses  of  Bald  and  Glastenbury  mountains. 

The  plateau  has  a  high  average  elevation.  "The  Dome"  in 
the  eastern  part  of  the  town  of  Pownal  is  2,750  feet  high,  while 
other  knobs  farther  east  in  Stamford  reach  an  elevation  of  3,000 
feet  or  more.  Bald  Mountain  northeast  of  Bennington  is  2,865 
feet  high ;  other  peaks  in  Glastenbury  Range  from  this  altitude  to 
3,764  feet  in  Glastenbury  Mountain. 

From  the  western  edge  of  the  Green  Mountain  Plateau  the 
descent  to  the  valley  is  very  steep  throughout  most  of  the  area. 
This  abrupt  topographic  break  is  a  striking  feature  of  the  land- 
scape. 

East  of  Bennington  the  western  margin  of  the  plateau  has 
been  offset  to  the  west  a  distance  of  two  miles.  This  east-west 
break  is  marked  by  the  course  of  Walloomsac  Brook.    Both  north 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  33y 

and  south  of  this  fault  the  western  margin  of  the  plateau  has 
practically  the  same  general  trend  to  the  north-northeast. 

By  this  same  offset  the  valley  is  shifted  to  the  east  at  Ben- 
nington. South  of  Bennington  the  valley  extends  in  a  somewhat 
southerly  direction,  gradually  narrowing  up,  and  ending  abruptly 
at  the  northern  end  of  Mason  Hill  in  the  town  of  Pownal. 

The  valley  which  comes  down  from  the  north  through  the 
towns  of  Manchester,  Sunderland,  Arlington  and  Shaftsbury  is 
bounded  on  the  west  by  a  high  range  which  terminates  west  of 
Shaftsbury  Center  in  West  Mountain  with  an  elevation  of  2,000 
feet.  The  valley  widens  out  as  it  enters  the  quadrangle,  its  west- 
ern margin  bending  west  around  the  southern  end  of  West  Moun- 
tain. Northwest  and  west  of  Bennington  is  a  wide-open  valley 
area  which  extends  west  beyond  the  limits  of  the  map. 

The  valley  south  of  Bennington  is  bounded  on  the  west  by 
the  Mount  Anthony  ridge.  This  ridge  begins  two  miles  west  of 
Bennington.  Its  eastern  margin  follows  a  southerly  course  as 
far  as  Pownal  Center.  Here  the  ridge  bends  to  the  southeast, 
cutting  off  the  valley  of  Bennington,  and  bringing  up  abruptly 
in  Mason  Hill  against  the  Green  Mountain  Range.  Mount  An- 
thony, southwest  of  Bennington,  is  2,345  feet  high.  The  elevation 
falls  off  southward  to  986  feet  at  Pownal  Center  and  rises  again 
through  1,500  feet  in  Mann  Hill  to  1,660  feet  in  Mason  Hill. 
The  North  Adams-Bennington  electric  railway  rises  from  the 
549  feet  contour  at  Pownal  village  to  an  altitude  of  986  feet  at 
Pownal  Center,  a  vertical  distance  of  437  feet  in.  about  three  miles, 
through  the  lowest  pass  in  this  mass  which  cuts  off  the  valley  of 
Bennington  at  the  south. 

Although  there  are  numerous  altitudes  in  the  valley  south  of 
Bennington  higher  than  this  pass,  the  essential  ridge-like  char- 
acter of  the  whole  stretch  from  Mount  Anthony  to  Mason  Hill  is 
reasonably  apparent,  its  former  relatively  higher  altitude  at 
Pownal  Center  being  obscured  by  the  erosion  of  the  mass  between 
Pownal  Center  and  the  bed  of  the  Hoosick.  The  Mount  Anthony 
portion  of  the  ridge  is  at  the  northern  end  of  a  southwardly  pitch- 
ing syncline.  This  fact  perhaps  in  connection  with  the  favor 
shown  by  the  forces  of  erosion  may  account  for  its  present  rela- 
tively higher  altitude. 

An  inspection  of  the  map  will  show  that  in  correspondence 
with  the  eastward  extension  of  the  valley  west  of  Bennington 
the  northern  end  of  the  Mount  Anthony  ridge  lies  farther  east 
than  does  the  boundary  of  the  valley  as  formed  by  West  Moun- 
tain in  Shaftsbury.  And  the  southeastward  bend  of  the  Mount 
Anthony  ridge  through  Mann  and  Mason  hills  finds  a  parallel  in 
the  great  eastward  sweep  of  the  valley  region  of  Williams- 
town  and  North  Adams  around  the  southern  end  of  Clarksburg 
Mountain  to  the  Hoosick  Range. 


340  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

DRAINAGE. 

In  southern  Vermont  and  northern  Massachusetts  the  Green 
Mountain  Range  is  the  divide  between  the  drainage  of  the  Hudson 
and  the  Connecticut  rivers. 

Hoosick  River,  which  rises  on  the  western  slope  of  the  Green 
Mountains  in  Massachusetts,  flows  north  to  North  Adams,  then 
westward  past  WilHamstown,  and  then  crosses  in  a  northwesterly- 
direction  the  extreme  southwestern  corner  of  the  state  of  Ver- 
mont. Five  miles  northwest  of  Hoosick  Falls  it  turns  west  to 
join  the  Hudson. 

Near  Hoosick  Junction,  N-.  Y.,  the  Hoosick  receives  the  waters 
of  Walloomsac  River  which  drains  the  larger  part  of  the  area 
discussed  in  this  paper.  The  Walloomsac  gathers  its  headwaters 
in  the  Green  Mountain  Range,  five  miles  east  of  Bennington,  from 
two  large  brooks,  one  of  which  forks  and  drains  the  southern 
slope  of  Glastenbury  Mountain,  while  the  other  forks  in  a  similar 
manner  and  drains  the  northern  slopes  of  Stamford  Mountain  in 
its  northern  extension  in  the  town  of  Woodford.  The  sources  of 
these  terminal,  tributary  streams  come  close  to  the  headwaters  of 
the  tributaries  of  the  Deerfield  River. 

North  of  Bennington,  Furnace  Brook  and  Paran  Creek  head 
on  a  low  divide  which  parts  the  drainage  of  the  Walloomsac  from 
that  of  the  Batten  Kill.  They  flow  south  to  join  the  Walloomsac. 
South  of  Bennington,  South  Stream  and  Jewett  Brook  flow  north 
from  Pownal,  the  former  receiving  the  drainage  of  the  western 
slope  of  Stamford  Mountain,  and  the  latter  that  of  the  eastern 
slope  of  Mount  Anthony.  South  Stream  and  Jewett  Brook  join 
near  Bennington  and  flow  into  the  Walloomsac  in  the  eastern  part 
of  the  town. 

The  western  slope  of  the  Mount  Anthony  ridge  drains  to  the 
Hoosick. 

In  general,  the  Walloomsac  has  an  east-west  direction  across 
the  gneiss,  quartzite,  limestone  and  schist.  Probably  its  course 
was  primarily  determined  by  certain  important  structural  features 
of  the  region. 

GENERAL  GEOLOGY. 

The  core  of  the  Green  Mountain  Range  is  made  up  of  gneiss 
of  pre-Cambrian  age. 

Time  did  not  allow  a  careful  examination  of  the  gneisses 
within  the  area.  It  was  extremely  difficult  to  accomplish  much 
on  the  mountains  of  the  range.  The  country  is  still  mostly  a 
heavily-wooded  wilderness  crossed  by  only  two  roads  and  a  few 
overgrown  trails.  Glastenbury  Mountain,  which  is  the  most  in- 
accessible, is  especially  disappointing  in  outcrops.  Seemingly  any 
separation  of  the  elements  of  its  pre-Cambrian  core  would  prove 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  341 

very  difficult  under  present  conditions.  Nevertheless,  the  writer 
had  hoped  to  make  some  study  of  these  rocks. 

It  would  seem  that  an  important  line  of  investigation  sup- 
plementary to  the  researches  of  various  workers  in  the  pre- 
Cambrian  rocks  of  the  Green  Mountain  belt  is  still  open.^  The 
difficulty  in  drawing  always  a  sharp  line  between  the  Cambrian 
and  the  pre-Cambrian  was  expressed  by  Professor  Pumpelly.^ 

Professor  Wolff  argued  for  the  presence  in  the  Cambrian 
("Vermont  Formation")  of  the  Hoosick  Range  of  coarse  gneisses, 
finer-grained  banded  gneisses,  shghtly  micaceous  gneiss,  meta- 
morphic  gneiss  conglomerate  and  ordinary  quartzite  conglomerate, 
these  rocks  or  phases  passing  into  one  another  along  the  strike.^ 
Later  Van  Hise*  made  the  white  gneiss  of  Hoosick  Mountain  pre- 
Cambrian  and  maintained  that  there  is  no  transition  between  the 
pre-Cambrian  igneous  and  the  Cambrian  sedimentary. 

Keith°  describes  as  a  result  of  recent  studies  in  Vermont  a 
great  thickness  of  schist,  dolomite,  graywacke,  quartzite  and  con- 
glomerate overlain  unconformably  by  the  Cambrian  quartzite 
which  transgresses  the  whole  of  the  lower  series.  This  series  is 
classed  as  Algonkian. 

Resting  against  the  gneiss  all  along  the  western  front  of  the 
range  within  the  area  is  a  lofty  brow  of  quartzite  which  slopes 
steeply,  often  precipitously,  to  the  valley  on  the  west.  This  quartz- 
ite is  a  conspicuous  feature  for  many  miles  northward  in  Ver- 
mont along  the  western  margin  of  the  Green  Mountain  Range. 

The  Woodford-Stamford  gneissic  core  of  the  Green  Moun- 
tain Range  extends  down  for  a  short  distance  into  Massachusetts 
and  terminates  in  Clarksburg  Mountain  directly  northwest  of 
North  Adams.  The  quartzite  formation  extends  from  the  town 
of  Pownal  southward  on  the  western  face  of  the  range  and  east- 
ward around  the  southern  slope  of  Clarksburg  Mountain.  It 
lies  unconformably  on  the  pre-Cambrian   (Stamford)  gneiss. 

In  the  quartzite  formation  "east  of  Bennington,"  and  also 
on  the  western  slope  of  Clarksburg  Mountain,  Dr.  C.  D.  Walcott" 
discovered  fossils  (Olenellus)  which  definitely  proved  the  quartz- 
ite to  be  of  Lower  Cambrian  age. 

On  the  east  of  Clarksburg  and  Stamford  mountains,  north 
from  North  Adams,  the  quartzite  extends  some  distance  north  of 
the  village  of  Stamford  through  Hartwellville  towards  Woodford. 
Its  further  northern  extension  was  not  followed. 

1 C.  p.  Berkey,  Structural  and  Stratigraphic  Features  of  the  Basal 
Gneisses  of  the  Highlands,  Bull.  N.  Y.  State  Mus.  107,  1907. 

A.  Keith,  A  pre-Cambrian  Unconformity  in  Vermont,  Bull.  Geol.  Soc. 
Amer.,  Vol.   25,  p.   39. 

2  Mon.  U.  S.  G.  S.,  XXIII,  p.  25. 

3  Idem,  pp.   35-118. 

*Bull.  U.  S.  G.  S.,  No.  360,  p.  588. 
^  Log.  cit. 

'5  The  Taconic  System  of  Emmens,  Amer.  Jour.  Sci.,  Series  3,  Vol.  XXXV, 
1888,  pp.  235-236. 


342  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

In  the  southern  part  of  the  area,  as  shown  on  the  map  of 
this  report,  the  quartzite  on  the  western  slope  of  the  range  hes 
against  the  schist  of  Mason  Hill,  and  north  of  Mason  Hill  against 
limestone  and  schist,  and  then  for  the  rest  of  the  distance  south 
of  Bennington  against  the  quartzite  formation  of  the  valley. 
Southeast  of  Bennington  the  floor  along  the  eastern  edge  of  the 
valley  is  quartzite.  It  extends  south  of  the  fault  along  Walloom- 
sac  Brook,  between  the  range  and  the  limestone  which  borders 
it  on  the  west,  and  wedges  out  to  the  south  against  the  edge  of 
the  plateau.  The  western  margin  of  the  range  cuts  somewhat 
diagonally  northeastward  across  the  general  trend  of  the  forma- 
tions of  the  valley,  south  of  Bennington. 

The  valley  quartzite  south  of  Bennington  is  bordered  by  a 
broad  limestone  band  which  extends  south  from  Bennington  and 
which  narrows  up  and  ends  somewhat  abruptly  at  the  south 
against  Mason  Hill.  The  limestone  gives  place  at  the  west  and 
south  to  the  schist  of  the  Mount  Anthony  ridge.  At  numerous 
places  along  the  eastern  slope  of  this  ridge,  north  of  Pownal 
Center,  the  limestone  is  seen  to  dip  westward  beneath  the  schist. 
It  appears  again  dipping  east  along  the  northwestern  slope  of 
Mount  Anthony.  It  forms  the  high  hill  just  east  of  the  village 
of  North  Pownal.  It  lies  on  the  schist  on'  the  west  side  of  the 
Hoosick,  two  and  a  half  miles  south  of  North  Pownal,  and  out- 
crops again  on  the  southwestern  slope  of  Mason  Hill  along  the 
Williamstown-Pownal  road  about  two  miles  southeast  of  Pownal. 

East-northeast  of  Bennington,  as  described  in  the  topog- 
raphy, the  plateau  has  suffered  an  offset  to  the  west  so  that  east 
of  Bennington,  south  of  Walloomsac  Brook,  the  quartzite  of  the 
valley  forms  a  recess  eastward,  while  north  of  the  stream  is  the 
steep  southern  slope  of  Bald  Mountain  and  the  western  quartzite 
slope  of  the  range  lies  two  miles  farther  west.  Northeast  of 
Bennington  from  the  Walloomsac  northward  to  Buck's  Cobble 
the  quartzite  was  traced  as  a  well-defined  band  about  two  miles 
wide  along  the  east  side  of  the  big  valley  and  east  and  north  of 
Buck's  Cobble  it  was  followed  somewhat  indistinctly  as  far  north 
as  Maple  Hill. 

The  same  sharp  topographic  break  which  marks  the  ascent 
from  the  valley  quartzite  to  that  which  fronts  the  range  south  of 
Bennington  also  distinguishes  the  relations  of  Glastenbury  Moun- 
tain to  the  valley  on  the  west.  North  from  Buck's  Cobble  the 
quartzite  is  replaced  by  sharply-folded  interbedded  limestones 
and  quartzite.  West  from  the  margin  of  the  valley  quartzite  and 
the  westernmost  scarps  of  the  hills  of  interbedded  limestones  and 
quartzites,  so  far  as  it  is  possible  to  learn  about  this  heavily  drift- 
covered  region,  the  valley  is  underlain  by  limestone  which  extends 
to  the  eastern  foot  of  West  Mountain  and  around  its  southern  end 
and  south  through  South  Shaftsbury  and  North  Bennington  to 
the  northern  end  of  Mount  Anthony.     West  of  North  Benning- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  343 

ton  the  limestone  is  mixed  somewhat  with  the  schist,  but  in  gen- 
eral bounds  the  schist  formation  at  the  west  much  as  shown  on 
the  map. 

The  quartzite,  limestone  and  schist  which  have  been  men- 
tioned form  the  eastern  members  of  the  great  Taconic  belt  of 
rocks  which  extends  from  northern  Vermont  southward  along 
and  near  the  boundary  of  New  England  and  New  York. 

As  early  as  1872  it  had  been  established  through  the  inves- 
tigations of  the  Rev.  Augustus  Wing  that  the  Hmestones  (Eolian) 
lying  west  of  the  Green  Mountain  Range  contained  strata,  as 
shown  by  fossils,  ranging  from  the  Upper  Potsdam  or  Lower 
Calciferous  to  the  Trenton.^  From  Wing's  investigations  the 
term  "Calciferous-Chazy-Trenton"  was  apphed  to  the  limestone 
in  general  as  it  outcropped  in  and  west  and  north  of  Rutland. 

Later  studies  in  the  limestones  of  Dutchess  County,  New 
York,  by  Professors  Dana  and  D wight  showed  the  presence  there 
of  the  Georgian,  Potsdam,  Calciferous  and  Trenton  in  rocks  hav- 
ing field  relations  similar  to  those  in  northern  Vermont  and  to  be 
regarded  as  essentially  the  southwestward  continuation  of  the 
Stockbridge  and  Eolian  limestone  formations  of  Massachusetts 
and  Vermont.^ 

In  1887,  Dr.  Walcott  carried  his  studies  into  the  region 
around  Bennington  and  southward  into  Massachusetts,  and  found 
fossils  in  the  limestone  which  he  assigned  to  the  Chazy-Trenton.'"^ 

By  these  and  other  researches  the  age  of  much  of  the  lime- 
stone of  the  Taconic  region  was  shown  to  be  of  Ordovician  age. 

In  1890,  Professor  Wolfif  studied  the  area  around  Rutland, 
Vt.*  He  found  the  limestone  (Eolian)  of  the  main  Rutland 
valley  to  lie  conformably  along  the  west  side  of  the  valley  on  the 
quartzite  of  Pine  Hill.  Pine  Hill  is  a  ridge  just  west  of  Rutland 
which  divides  the  main  limestone  valley  of  Rutland  from  a 
smaller  limestone  valley  in  Center  Rutland.  Wolfif  found  the 
quartzite  forming  the  eastern  slope  of  Pine  Hill  to  bend  to  the 
eastward  north  of  Rutland  and  join  the  quartzite  of  the  main 
range.  At  Pine  Hill  the  quartzite  passes  upward  into  limestone 
through  beds  of  "calcareous  quartzite."  Cambrian  fossils  were 
found  in  the  limestone  above  the  contact  with  the  quartzite. 
Associated  with  the  quartzite  of  Pine  Hill  was  a  series  similar 
or  identical  with  that  associated  with  the  quartzite  east  of  the 
valley,  in  each  case  older  than  the  limestone.  The  limestone  of 
the  Center  Rutland  valley,  just  west  of  Pine  Hill,  as  shown  by 
fossils  is  of  Ordovician  age.  The  general  significance  of  these 
relations  will  be  appreciated.  Part  of  the  Eolian  limestone  near 
Rutland  was  thus  indicated  to  be  of  probably  Lower  Cambrian 
age. 

1  Amer.  Jour.  Sci.,  Series  3,  Vol.  IV,  1872  ;  Vol.  XIII,  1877. 

2  Papers  by  W.   B.   Dwight,   Amer.   Jour.    Sci.,   1879-1889. 

3  Amer.  Jour.  Sci.,  Series  3,  Vol.  XXXV,  1888,  p.   238. 
*BulI.  Geol.  Soc.  Amer.,  1891,  pp.  331-337. 


244  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

The  schists  which  he  to  the  west  of  the  hmestone  of  the 
Vermont  valley,  extending  north  from  West  Mountain  in  Shafts- 
bury  through  East  Poultney  and  beyond,  were  colored  Cambrian 
by  Walcott^  in  a  map  accompanying  his  discussion  of  The  Taconic 
System  of  Emmons,  while  the  Mount  Anthony  ridge  and  the 
schists  to  the  west  of  it  and  around  Hoosick  Falls,  together  with 
certain  schist  outliers  in  the  limestone  of  the  valley  between 
Shaftsbury  and  Rutland,  were  shown  as  belonging  to  the  Hudson 
terrane. 

In  Pownal,  at  what  appears  from  the  description  and  the 
map  to  be  on  the  southwestern  side  of  the  Mason  Hill  mass, 
Walcott  discovered  fossils  which  he  described  as  Trenton,  and 
again  on  the  east  side  of  Mount  Anthony,  about  three  miles  south 
of  Bennington  Center,  in  the  limestone  beneath  the  schist,  he 
found  parts  of  crinoids  allied  to  a  form  found  in  the  Trenton 
limestone  of  New  York.  Near  Hoosick  Falls,  in  limestone  about 
200  feet  below  the  "shales,"  he  found  fossils  of  the  genera 
Maclurea  and  Murchisonia  and  assigned  the  limestone  to  the 
Chazy-Trenton.  On  the  basis  of  these  discoveries,  the  schist  of 
Mount  Anthony  and  the  region  about  Hoosick  Falls  was  placed 
in  the  Hudson  terrane  and  considered  to  be  of  Ordovician  age. 

The  terrigenous  sediments,  described  above  as  colored  on 
Walcott's  map  as  Georgian,  were  so  designated  on  the  basis  of 
fossils  of  Lower  (then  called  Middle)  Cambrian  age,  contained 
in  thin  interbedded  limestones.  These  fossils  were  "distributed 
at  various  horizons  throughout  the  14,000  feet  or  more  of  strata 
referred  to  this  terrane."  These  slaty,  or  phyllitic  rocks  Walcott 
regarded  as  the  off-shore  equivalent  of  the  quartzite  of  the  Green 
Mountain  Range.  Two  belts  of  the  Cambrian  slates  are  shown 
with  a  belt  of  the  Hudson  terrane  faulted  in  between  them. 

Probably  most  of  the  eastern  portion  of  Walcott's  eastern 
Georgian  belt,  including  West  Mountain,  is  of  Ordovician  age. 

GENERAL  RELATIONS  OF  GEOLOGY  AND 
TOPOGRAPHY. 

The  whole  region  is  mountainous  in  structure.  Viewing  it 
as  a  whole,  we  find  that  the  mountain  folds  have  been  truncated, 
exposing  the  older  rocks  along  the  anticlinal  axes,  while  in  the 
synclinoria  the  younger  strata  were  folded  down  and  thereby  pre- 
served. In  the  valleys  certain  strata,  which  primarily  belonged  to 
faulted  upthrust  blocks,  have  been  dropped  back  by  normal  ad- 
justment faulting  and  are  now  exposed  by  erosion  in  abnormal 
relation  to  adjacent  strata. 

Professor  Davis-  early  described  the  region  as  a  Avorn-down 
mountain  area  peneplaned  by   sub-aerial  agencies.     The  higher 

1  Amer.  Jour.  Sci.,  Series  3,  Vol.  XXXV,  1888. 
siMon.  Nat.  Geogr.  Soc,  Vol.   1,  1895,  pp.   279-284. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


345 


eminences  were  interpreted  as  monadnocks.  Professor  Dale^ 
later  questioned  the  peneplaned  character  of  the  Taconic  physi- 
ography on  the  ground  that  the  peneplain  theory  would  require 
for  the  region,  as  shown  by  its  history,  an  elevation  of  from  1,500 
to  2,000  feet  at  the  beginning  of  the  Tertiary  and  that  subsequent 
time  was  seemingly  not  long  enough  to  carve  to  its  present  con- 
dition a  dissected  peneplain,  if,  as  seemed  likely,  such  sculpture 
involved  the  removal  of  at  least  half  of  the  Taconic  topographic 
belt  since  its  post-Ordovician  elevation. 

Recently  Professor  BarrelP  has  come  forward  with  the  view 
that  much  of  the  Piedmont  belt  of  southern  New  England  and 
New  Jersey,  which  is  generally  regarded  as  part  of  a  great  pene- 
planed region,  could  be  explained  as  the  result  of  marine  plana- 
tion  at  right  angles  to  the  lines  of  drainage.  In  western  Massa- 
chusetts and  Connecticut  and  extending  into  New  York  and 
southward,  he  has  described  a  more  or  less  clearly  recognizable 
series  of  wave-cut  terraces  at  different  levels,  showing  the  former 
presence  of  the  sea,  at  the  time  of  its  maximum  transgression,  a 
long  distance  inland  from  the  margin  of  the  present  coastal  plain. 
He  correlates  the  terraces  with  definite  formations  of  the  present 
coastal  plain  and  recognizes  in  the  planes  of  disconformity  among 
the  deposits  of  the  present  plain  the  record  of  the  uplifts  that 
successively  elevated  the  different  terraces,  assuming,  of  course, 
that  the  oscillitary  movement  reached  the  coastal  plain. 

Condensed   Table  of  Hard  Rock   Formations. 


Age. 


Cambro- 
Ordovician. 


Basal  Cambrian. 


Pre-Cambrian. 


Formation. 


Schist. 


Limestone. 


'Vermont   Formation." 
Unconformity. 


Members. 


Shales. 

Slates. 

Grits,  Phyllites. 

Calcareous  Schists. 

Sericite  Schist. 

Marbles. 

Compact  and  granular 
crystalline  limestones. 

Limestones  and  calcareous 
quartzites  with  inter- 
bedded  quartzite. 

Quartzite. 

Quartzitic  schist. 

Schistose  quartzite. 
Dense  compact  quartzite. 
"Granular  quartz  rock." 
Conglomerate. 

Gneiss  of  Stamford  Moun- 
tain and  Harmon  Hill. 


1  Bull.  U.  S.  G.  Sur.  No.  272,  p.  33. 

2  Bull.  Geol.  Soc.  Amer.,  Vol.  24,  pp.  688-690. 


346  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

At  the  time  of  its  farthest  advance  the  sea  is  believed  to  have 
reached  the  south  side  of  the  Adirondacks  and  the  southeastern 
side  of  the  Green  Mountains  in  Massachusetts,  there  cutting  the 
oldest,  or  "Becket  terrace"  in  middle  Cretaceous  time.  Later  ter- 
races range  from  this  epoch  into  the  Pleistocene. 

The  absence  of  unconsolidated  marine  deposits  far  inland 
from  the  margin  of  the  present  coastal  plain  is  held  not  to  in- 
validate the  claims  of  this  later  view  of  the  Piedmont  region, 
since  such  deposits  might  well  have  been  almost  completely  if 
not  quite  removed  by  erosion. 

The  approximate  elevation  of  the  inner  margin  of  the  oldest, 
or  Becket  terrace,  is  now  2,400  feet,  but  the  region  is  known  to 
have  undergone  progressive  warping. 

THE  GNEISS  AND  ASSOCIATED  QUARTZITE. 

GENERAL  DESCRIPTIOiV. 

The  gneiss  was  examined  on  the  western  slope  of  "The 
Dome"  and  on  the  western  and  northern  slopes  and  summit  of 
Harmon  Hill.  The  western  boundary  of  the  gneiss,  where 
shown,  is  drawn  in  somewhat  arbitrarily.  The  boundary  was  not 
touched  on  Bald  or  Glastenbury  mountains. 

On  the  southwestern  side  of  "The  Dome"  the  quartzite  rests 
unconformably  on  the  gneiss.  West-southwest  of  this  eminence, 
lower  down  the  slope  and  about  on  the  1,700-foot  contour,  in  a 
valley  recess  southeast  of  the  pond,  the  gneiss  is  exposed  in  a 
wet-weather  gulley.  The  rock  is  in  place,  but  the  strike  and  dip 
of  the  foliation  could  not  be  satisfactorily  determined.  North- 
ward from  this  outcrop  along  the  steep  slope  east  of  the  pond, 
gneiss  talus  boulders  were  common  with  some  admixture  of 
quartzite  northward. 

At  a  point  due  east  from  the  pond,  well  up  the  very  steep 
slope  at  this  point,  limestone  and  interbedded  calcareous  quartzite, 
quite  like  that  which  will  presently  be  described  as  commonly 
occurring  apparently  at  no  great  distance  above  the  quartzite  of 
the  valley  south  and  north  of  Bennington,  forms  the  slope  with 
strike  N.  17°  E.  and  dip  25°  easterly.  This  limestone  at  a  short 
distance  to  the  northeastward  passes  upward  into  black,  shiny, 
graphitic-looking  schist,  or  phyllite,  which  forms  the  summit  of 
the  sharp  spur  that  sticks  out  northeastward  from  the  range  in 
the  direction  of  Barber's  Pond.  Descending  this  spur  towards  its 
apex,  the  phyllite,  which  seems  to  be  conformable,  gives  place  to 
limestone  and  interbedded  quartzitic  layers  like  those  described 
above.  The  phyllite  is  less  gritty  than  the  schist  of  Mason  and 
Mann  hills,  and  differs  somewhat  from  any  which  I  have  else- 
where observed  in  the  area.  I  have  not  elsewhere  found  it  asso- 
ciated with  these  particular  limestone  beds  as  shown  in  this  spur. 
The  relations  are  peculiar  and  difficult  of  explanation.     The  phyl- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  347 

lite  apparently  lies  in  a  syncline  of  limestone  closed  northwest- 
ward and  pitching  towards  the  range.  Northwest  of  the  log 
cabin  the  limestone  beds  stand  at  high  angle. 

I  have  drawn  a  fault,  from  the  outcrop  of  gneiss  mentioned 
above,  north-northeastward  where  this  spur  abuts  against  the 
range  to  show  the  prevailing  tendency  of  the  older  rocks  to  appear 
against  the  younger  by  reverse  faulting.  To  what  extent  the 
older  rocks  moved  upward  will  be  discussed  later  on.  This  spur 
is  mentioned  in  connection  with  the  gneiss  as  it  helps  to  develop 
the  writer's  interpretation  of  the  structural  relations  along  the 
western  margin  of  the  range. 

Northeast  of  this  spur  is  another  sharp  recess,  on  the  eastern 
edge  of  which  ascends  the  road  that  crosses  the  range  to  Stam- 
ford. Along  this  road  just  before  it  makes  the  abrupt  turn  up 
the  steeper  slope  of  the  mountain  limestone  outcrops  in  the  road. 
Definite  readings  could  not  be  made.  The  limestone  is  not 
succeeded  by  any  outcrop  along  the  road  for  a  long  distance. 
Near  the  summit  thin-bedded  quartzite  with  irregular,  rusty  part- 
ing surfaces  outcrops  in  the  road  and  woods  with  low  westerly 
dip. 

North  of  the  mountain  road  to  Stamford  the  western  slope 
of  the  range  is  quartzite  above  the  lower  drift-covered  portion. 
It  was  observed  at  places,  in  the  woods,  dipping  gently  westward 
and  in  some  places  lying  nearly  flat.  Near  the  summit  the  thin- 
bedded  quartzite  was  observed  passing  upward  into  gritty  schist 
which,  in  some  places  showed  great  similarity  to  certain  lower 
members  of  the  schist  formation  overlying  the  limestone  in  Mount 
Anthony. 

The  valley  occupied  by  the  pond  northwest  of  the  gneiss 
outcrop,  which  was  described  above,  is  apparently  underlain  by 
limestone,  but  south  of  this  recess  the  quartzite  of  the  range 
extends  a  half  mile  or  more  west  of  the  outcrops  of  gneiss  and 
along  Reservoir  Brook  abuts  against  the  schist  of  Mason  Hill. 
The  quartzite  stands  as  a  fairly  high  scarp  above  the  brook  about 
one  mile  north  of  the  Williamstown  reservoir.  At  this  place  it 
is  a  thick-bedded,  compact  white  rock.  Higher  up  the  brook  it 
becomes  more  thinly-bedded  and  the  scarp  in  consequence  dimin- 
ishes in  abruptness  to  the  northward.  Where  the  scarp  is  com- 
posed of  the  compact  heavy  quartzite,  we  have  exposed  lower 
beds  of  that  formation.  The  dip  is  flat,  or  slightly  easterly.  The 
general  relations  are  shown  in  figure  27. 

Along  the  mountain  road  east  of  Reservoir  Brook  and 
between  the  brook  and  road  are  frequent  low-lying  ledges  of  the 
thin-bedded  quartzite,  having  a  notably  flattish  position.  The 
quartzite  is  often  rather  a  quartzite-schist  with  well-developed 
micaceous  bands.  Ledges  are  often  "flaggy"  and  under  the 
hammer  break  into  irregular  chips  with  rusty  parting  planes. 
Along  the  brook  east  of  the  mountain  road,  at  the  base  of  the 


348  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Steeper  slope  on  the  west  of  the  southward  extension  of  "The 
Dome,"  it  changes  to  a  fine-grained  quartz-pebble  conglom- 
erate. Along  the  mountain  road  just  before  it  leaves  the 
woods  at  the  north,  just  east  of  the  source  of  Reservoir  Brook, 
the  thin-bedded  quartzite  is  badly  crumbled  and  frequently  carries 
veinlets  of  quartz.  East  of  these  outcrops  is  the  thin-bedded, 
flaggy  quartzite  which  prevails  over  most  of  this  flat  hill  lying 
southwest  of  "The  Dome." 

Along  the  higher  portion  of  the  western  slope  of  the  range 
the  quartzite,  as  far  as  the  physical  difficulties  made  it  possible, 
was  traced  from  Roaring  Branch  to  the  southern  end  of  Harmon 
Hill.  On  the  western  slope  of  this  hill  the  gneiss  comes  down 
close  to  the  base  and  stands  in  ledges  from  30  to  40  feet  above 
the  quartzite.  The  contact  is  clearly  a  faulted  one.  Here  the 
upthrust  brought  the  gneiss  against  the  quartzite,  as  now  exposed. 
The  quartzite  dips  slightly  to  the  westward  and  passes  by  gradual 
slope  into  the  valley  west  of  the  hill. 

The  actual  contact  of  gneiss  and  quartzite  was  not  observed, 
but  ledges  of  the  two  formations  are  less  than  100  feet  apart. 
The  quartzite  strikes  nearly  north,  or  slightly  west  of  north,  while 
the  strike  of  the  foliation  of  gneiss  is  east  of  north.  The  rela- 
tions here  described  are  best  observed  in  the  pasture  about  one- 
half  mile  northeast  of  Woodward's  Corner. 

The  fault  between  the  gneiss  and  quartzite  I  have  repre- 
sented as  dying  away  southward  in  the  quartzite,  its  place  being 
taken  by  another  break  farther  west  which  faulted  the  quartzite 
of  the  range  against  that  of  the  valley. 

From  its  outcrops  near  the  quartzite  along  the  fault,  the 
gneiss  continues  up  the  slope  to  the  summit  of  the  hill.  A  read- 
ing at  the  summit  gave  the  strike  of  the  foliation  as  N.  60°  E. 
and  the  dip  80°  NW. 

The  relatively  ancient  character  of  the  foliation  of  the  gneiss 
is  impressive.  It  seemingly  antedates  the  deposition  of  the 
quartzite,  as  shown  by  the  discordance  in  strike  and  dip,  and 
belongs  to  a  pre-Cambrian  mountain-building  time.  The  gneiss 
had  acquired  practically  its  present  fohated  condition  before  the 
deposition  of  the  quartzite. 

East  of  Bennington,  in  the  valley  along  the  Woodford  road 
which  skirts  the  northern  end  of  Harmon  Hill,  the  quartzite  out- 
crops in  frequent  ledges.  Less  than  a  mile  east  of  the  trestle 
bridge  across  the  Walloomsac  the  road  has  been  blasted  through 
a  heavy  ledge  of  quartzite  which  rises  abruptly  from  the  bed  of 
the  brook.  This  ledge  is  nearly  along  the  northward  projection 
of  the  quartzite  just  west  of  the  fault  at  Harmon  Hill.  It  also 
probably  lies  south  of  the  cross  fault,  which  is  represented  on 
the  map  as  cutting  off  the  Bald  Mountain  mass  at  the  south. 

Numerous  ledges  of  the  quartzite  outcrop  along  the  road  to 
the  eastward.     This  formation  was  traced  from  the  fork  in  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  349 

road,  along  Walloomsac  Brook  to  the  junction  of  Bickford 
Hollow  and  Bolles  brooks,  and  also  beyond  the  forks  along  City 
Stream  for  three-fourths  of  a  mile.  Along  the  upper  reaches 
of  the  Walloomsac  the  quartzite  is  the  rusty,  flaggy  rock  which 
has  been  described. 

A  mile  from  the  fork,  along  the  Woodford  road,  the  gneiss  of 
Harmon  Hill  outcrops  in  the  road,  showing  the  foliation  strike 
as  N.  50°  E.  and  the  dip  70°  E.  The  quartzite  was  not  traced 
farther  east. 

It  seems  likely  that  a  great  irregular  fault  cuts  off  the  gneiss 
of  Harmon  Hill  at  the  northern  end,  and  that  this  formation  rests 
with  faulted  contact  against  the  quartzite  in  the  valley  north  of 
the  hill. 

PETROGEAPHY  OF  THE  HARMOJ^  HILL  GNEISS. 

The  gneiss  as  it  appears  along  the  Woodford  road  is  a  rather 
fine-grained  biotite  gneiss  without  pronounced  foliation.  The 
biotite  appears  in  fine  flakes  uniformly  distributed  in  the  rock 
both  across  and  with  the  foliation.  The  thin  section  shows  a 
granitoid  texture  with  prominent  anhydrous  of  feldspar  and 
quartz  of  allotriomorphic  type  with  biotite  of  igneous  habit  and 
distribution,  usually  enclosed  in  the  feldspars.  The  feldspars 
are  somewhat  decomposed  and  are  partly  clouded  with  kaolinite 
and  other  decomposition  products. 

The  gneiss  at  times  carries  coarser  bands  of  quartz  and  feld- 
spar which  roughly  alternate  with  micaceous  bands  of  a  texture 
similar  to  the  finer-grained  gneiss  described  above.  Where 
freshest  the  feldspars  appear  to  be  chiefly  plagioclase.  Zircon 
occurs  as  an  accessory.  There  appear  to  be  no  pronounced  strain 
effects.  While  there  is  usually  a  decided  wavy  extinction  of  the 
quartz,  the  twinning  lamellae  of  the  feldspars  are  not  broken  per- 
ceptibly and  show  uniform  width  along  their  entire  lengths. 

The  rock  at  the  top  of  the  hill  is  essentially  the  same  as  that 
along  the  Woodford  road,  although  it  is  more  prominently 
gneissic.  It  has  the  same  general  texture  in  thin  section  and  the 
same  mineralogy,  with  the  addition  of  some  microcline. 

The  rock  near  the  contact  with  the  quartzite  along  the  west- 
ern slope  of  the  hill  clearly  shows  the  effect  of  shearing.  In  the 
hand  specimen  it  appears  crushed  and  when  hit  by  the  hammer 
breaks  along  smoothed  surfaces.  In  thin  section  the  quartz  ap- 
pear shattered.  The  fragments  have  recrystallized  and  healed 
without  extensive  migration.  Where  before  were  large  quartz 
crystals  are  now  patchworks  of  small  grains  with  independent 
extinction.  The  plagioclase  shows  badly  bent  and  pinched  out 
lamellae  and  the  biotites  are  broken  into  numerous  fragments 
and  dustings. 


350 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


INTERPRETATION. 

So  far  as  I  have  observed,  there  is  Httle  evidence  of  folding 
in  the  gneiss  and  not  much  of  shearing,  except  in  the  zone  of 
faulting. 

From  the  gentle  dip  of  the  quartzite  and  its  frequent  almost 
flat  position  we  may  suppose  that  this  formation,  as  a  general 
rule  was  not  violently  folded.  At  places  accommodation  was 
effected  in  the  gneiss  by  shearing,  but  over  large  areas,  so  far  as 
observed,  even  shearing  is  inconspicuous.  The  quartzite  was 
folded  somewhat  in  the  general  movement  of  elevation  and  in 
some  places  buckled  into  small  folds,  as,  for  example,  along  lines 
on  which  the  gneiss  was  shoved  up  on  the  quartzite,  the  break 
often  dying  away  along  the  line  into  a  fold  in  the  quartzite. 

The  breaks  were  primarily  initiated  by  the  crystalline  gneissic 
substratum  refusing  to  fold.  The  tendency  to  rupture  was  doubt- 
less augmented  by  the  covering  of  heavy  quartzite  which  was 
also  reluctant  to  fold. 

The  release  of  the  highly  crystalline  substratum  was  ap- 
parently effected  by  numerous  breaks  along  the  strike.  At  some 
places,  for  some  reason,  the  rupture  occurred  earlier  than  at 
others  and  at  some  places  farther  west,  so  to  speak,  than  at  others, 
the  effect  being  a  sort  of  echelon  of  faults  along  the  western 
margin  of  the  range. 


Figure    26. — Generalized   section   to   show  reversed   fault   between   the   gneiss 
and  quartzite  on  the  west  of  Harmon  Hill. 

The  fault  on  the  west  of  Harmon  Hill,  figure  26,  is  repre- 
sented as  dying  away  southward  in  the  quartzite.  Its  place  is 
taken  by  another  break  farther  west  by  which  the  quartzite  rests 
against  younger  quartzite  at  the  west.  The  latter  fault  is  rep- 
resented as  dying  away  northward  in  the  quartzite  west  of  Har- 
mon Hill.  Southward  it  is  drawn  near  the  base  of  the  slope  as 
far  south  as  the  latitude  of  Barber's  Pond.  It  then  probably 
merges  with  a  break  that  bounds  the  valley  quartzite  south  of 
Bennington  on  the  west  or  passes  directly  into  the  fault  shown 
along  the  western  slope  of  "The  Dome." 

The  fault  on  the  west  of  "The  Dome"  dies  away  southward, 
its  place  being  taken  by  another  break  farther  west  by  which  the 
quartzite  was  thrown  against  the  schist   of   Mason   Hill  along 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


351 


Reservoir  Brook.     My  interpretation  of  the  probable  relations  at 
Mason  Hill  are  shown  in  figure  27.     The  famous  "Sand  Springs," 


,....-' ''^^<^:^ 

''  '     ■  ^-^'^^^^'^y^^  "^  "^       "^  "^          ''  •/ 

'€"u''''l^^'/'y''y/^y:- 

-  -  v^^^^tA^J'i>/_^-;v!;<^  y  ^  ■/    J  J     ^    J     ■'      ^ 

rv 

r_: 

^^^^^^^^^^^V/fr^'^^  "  ^  ^GTie-fss".   ^   ^  ./  " 

Sc7i  >si' 

7^==^^Pff^ :'>y/ ' :: ' :  -^■' "-/- -- ^-i 

Figure   27. — Generalized  section  to  show  the  interpretation  of  the  relations 

at  Mason  Hill. 

a  resort  two  miles  northwest  of  Williamstown,  lies  along  or  close 
to  the  southward  extension  of  the  Mason  Hill  fault  along  Reser- 
voir Brook.  This  spring  issues  from  clear  white  sand  and  in  win- 
ter and  summer,  as  well  as  in  dry  and  wet  seasons,  gives  an  average 
flow  of  400  gallons  a  minute.  The  temperature  of  the  water  in 
winter  and  summer  is  about  76°  Fah.  Its  freedom  from  organic 
contamination  and  its  remarkable  mineral  content  have  given  the 
water  a  wide  reputation  for  medicinal  purposes,  both  for  drink- 
ing and  bathing.  The  water  is  now  extensively  used  for  the 
manufacture  of  "soft  drinks,"  and  the  excess  flow  is  utilized  for 
a  swimming  pool.  The  following  analysis  was  made  by  Leverett 
H.  Mears,  Professor  of  Chemistry  at  WiUiams  College. 

Parts  per  100,000. 

Lithium    chloride    0.0353 

Sodium  chloride 0768 

Acid  calcium  carbonate   3.2249 

Acid  magnesium  carbonate  2.6479 

Calcium  sulphate   7262 

Aluminium  sesquioxide 0325 

Iron  sesquioxide 0075 

Silica    7026 

Sodium  carbonate    4641 


7.9178 


The  spring  issues  from  the  drift,  but  its  constancy,  tempera- 
ture and  mineral  content  suggest  a  deep-seated  source  and  argue 
for  the  great  depth  of  the  fault  along  which  it  comes. 

The  fault  shown  on  the  map  as  bordering  the  quartzite  of  the 
range  on  the  west  of  the  low  hill  just  southwest  of  Harmon  Hill  is 
marked  by  a  rugged  talus  slope  across  the  edge  of  the  quartzite 
beds  just  within  the  edge  of  the  woods  southwest  of  Woodward 
Corner  and  Harmon  Hill.  This  scarp  and  talus  was  distinctly 
followed  southward  for  two  miles. 

There  would  have  been  a  tendency  to  break  across  the  strike 
on  the  north  of  this  hill,  but  it  seems  more  likely  that  the  fault 


352  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

on  the  west  dies  away  northward  owing  to  compensation  by  the 
fault  at  the  east  on  the  west  of  Harmon  Hill. 

Southwest  of  "The  Dome,"  however,  there  may  be  a  cross 
fracture  for  here  the  quartzite  passes  northward  into  limestone. 
This  limestone  may,  however,  be  of  Cambrian  age  as  discussed 
beyond. 

The  "valley  quartzite"  is  represented  as  probably  wedging 
out  to  the  southward  against  the  range.  The  quartzite  of  the 
range  cuts  somewhat  diagonally  across  the  general  trend  of  the 
formations  in  the  valley. 

The  presence  of  the  quartzite  formation  high  up  on  the 
slopes  of  the  range  and  its  eastward  extension  along  Walloomsac 
Brook  in  themselves  strongly  argue  for  the  former  extension 
of  this  formation  over  the  range  toward  Woodford.  The  quartz- 
ite, as  noted  in  the  discussion  of  the  general  geology,  extends 
northward  from  the  southern  end  of  Clarksburg  Mountain  for  a 
long  distance  toward  Woodford  on  the  east  of  Stamford  Moun- 
tain. The  presence  of  the  quartzite  formation  along  the  head- 
waters of  the  Walloomsac  and  in  City  Stream  may  be  explained 
by  down-faulting. 

THE  VALLEY  QUARTZITE  SOUTH  OF  BENNINGTON. 

By  this  term  may  be  understood  the  quartzite  formation  as 
it  outcrops  in  the  valley  west  of  the  prominent  gneiss  or  quartzite 
scarps  and  slopes  of  the  range. 

East  of  Bennington  outcrops  are  concealed  by  modified  drift 
as  far  east  as  the  foot  of  Harmon  Hill  and  the  outcrop  along  the 
Woodford  road  a  mile  east  of  the  bridge  across  the  Walloomsac. 

South  of  Walloomsac  Brook  the  only  outcrop  observed 
between  the  range  and  South  Stream  was  two  and  a  half  miles 
south  of  the  brook,  so  effectually  are  outcrops  concealed  by  the 
heavy  surface  deposits  over  this  area.  Near  the  south  road  to 
Sucker  Pond,  about  half  way  between  the  foot  of  the  range  and 
the  old  lumber  mill  along  South  Stream,  where  this  road  makes 
its  sharp  bend  southward,  are  outcrops  of  quartzite. 

Drift  conceals  this  formation  between  these  outcrops  and 
South  Stream.  In  the  bed  of  the  latter,  near  the  bridge,  a  fourth 
of  a. mile  north  of  the  old  lumber  mill,  the  quartzite  gives  a  strike 
of  N.  42°  E.  and  a  dip  of  17°  SE.  From  the  bed  of  the  stream 
the  topography  eastward  rises  by  gentle  slope  to  the  foot  of  the 
range.  Near  the  old  lumber  mill  the  limestone  is  interbedded 
with  calcareous  quartzite  at  the  dam  and  in  and  west  of  the  road 
just  above  the  stream.  Similar  beds  outcrop  along  the  stream 
at  the  gentle  rapids  five  or  six  hundred  yards  south  of  the  dam. 
All  the  beds  along  the  stream  have  a  notably  flattish  position. 

The  valley  quartzite  and  its  associated  interbedded  series 
were  not  traced  farther  south,  but  probably  continue  under  the 
drift  for  a  distance  of  three  or  more  miles  southward  to  the  foot 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  353 

of  the  range,  seemingly  wedging  out  where  the  Hmestone  extends 
down  into  the  recess  southeast  of  Barber's  Pond. 

Northward  along  the  road  that  follows  South  Stream  to 
Bennington,  about  three-fourths  of  a  mile  north  of  the  old  lumber 
mill,  the  interbedded  calcareous  quartzite  and  Hmestone  outcrop 
in  the  bed  of  the  stream  and  on  each  bank.  The  beds  vary  from 
two  to  four  to  six  inches  in  thickness  and  dip  gently  eastward ; 
a  stratum  of  limestone  beds  alternating  with  a  stratum  of  cal- 
careous quartzite.  The  road  to  Bennington  forks  just  north  of 
these  outcrops.  At  the  fork  a  ledge  of  quartzite  was  blasted  to 
make  way  for  the  road.  The  quartzite  in  this  ledge  is  sheared 
vertically,  apparently  at  right  angles  to  the  bedding,  which,  how- 
ever, is  obliterated,  and  along  the  shearing  planes  are  numerous 
crystals  of  pyrite  which  have  stained  the  sheared  surfaces  a  rusty 
brown.  The  five  feet  of  vertical  exposure  here  is  all  dense  steel- 
blue  quartzite.  Two  or  three  outcrops  of  the  quartzite  were 
noted  farther  north  along  the  east  road  from  this  fork. 

The  data  are  meager  for  forming  definite  conclusions,  but 
from  the  sheared  quartzite  just  described  and  the  general  flat 
position  of  the  beds,  I  imagine  the  valley  quartzite  to  have  buckled 
very  little,  but  on  the  contrary,  to  have  faulted  against  the  rocks 
farther  west.  In  the  course  of  adjustments  following  reverse 
faulting  it  would  probably  have  dropped  back  again  by  normal 
faulting  along  earlier  thrust  planes  so  that  its  present  position 
w^ould  be  misleading  as  to  its  real  history.  The  valley  quartzite 
east  of  Bennington  would  have  folded  with  that  of  the  range  until 
the  great  breaks  along  its  eastern  and  northern  margin  occurred 
when  it  would  have  slumped  somewhat.  The  amount  of  displace- 
ment of  the  valley  quartzite  along  its  western  margin  would  have 
been  less  than  that  which  occurred  in  the  quartzite  and  gneiss 
of  the  range  on  the  principle  that  the  reverse  faulting  would  tend 
to  die  away  westward. 

THE  VALLEY  QUARTZITE  AND  INTERBEDDED  LIME- 
STONES AND  QUARTZITE  NORTH  OF 
BENNINGTON. 

Northwest  of  Bennington  on  the  south  bank  of  the  Wal- 
loomsac,  at  the  edge  of  the  golf  links  of  the  Mount  Anthony  Golf 
Club,  near  the  covered  bridge,  quartzite  is  interstratified  with 
limestone,  the  whole  forming  a  gentle  arch.  At  this  place  there 
is  no  shearing  and  the  outcrop  is  considered  to  lie  east  of  the 
probable  western  boundary  of  the  valley  quartzite  in  its  occurrence 
north  of  Bennington. 

A  mile  and  a  half  north  of  the  outcrops  at  the  golf  links 
along  the  road  to  South  Shaftsbury,  the  quartzite  outcrops  in  the 
road.  North  of  this  outcrop  two  roads  leave  the  South  Shafts- 
bury  road,  one  going  west,  the  other  east.     On  the  latter,  close  to 


354 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


the  main  road  and  south  and  north  of  it,  ascending  the  slope  to 
the  eastward,  are  numerous  ledges  of  the  quartzite  lying  nearly- 
flat,  or  dipping  gently  eastward.  This  road  is  locally  known  as 
the  "Stony  Hill  road." 

An  almost  continuous  outcrop  of  the  quartzite  was  traced 
northward  through  the  woods  along  the  edge  of  the  hill,  one- 
fourth  of  a  mile  east  of  the  South  Shaftsbury  road,  for  nearly  a 
mile.  Westward  the  quartzite  descends  by  gentle  slope  to  the 
South  Shaftsbury  road,  but  the  slope  is  across  the  edges  of  the 
quartzite  beds.     Eastward  the  formation  passes  under  drift. 

North  of  the  next  crossroad,  the  quartzite  forms  a  high 
hill  just  northwest  of  Wait's  Corner.  Well  up  the  rather  steep 
eastern  slope  of  this  hill  are  great  patches  of  white  granular 
quartzite  dipping  easterly.  The  southern  end  of  this  hill  is  a 
berry  pasture.  North  of  the  pasture  are  thick  woods  with  some 
clearings.  Through  this  wood  the  quartzite  was  followed  nearly 
to  the  next  crossroad  running  from  South  Shaftsbury  to  the 
Madison  school.  The  northernmost  outcrop  of  the  quartzite,  as 
thus  followed  from  Bennington  northward  was  noted  near  Buck's 
Corner.  North  of  the  South  Shaftsbury  crossroad  begins  the 
southern  limestone  slope  of  Buck's  Cobble.  The  limestone  con- 
tinues northward  through  Harrington  Cobble  and  across  the  next 
road  and  then  passes  under  a  gentle  west  slope,  lying  between 
Harrington  Cobble  and  the  crossroad  which  skirts  Trumbull 
Mountain  on  the  south. 

East  of  the  north-south  road  on  the  east  of  Buck's  Cobble, 
everything  is  concealed  by  drift  as  far  north  as  Maple  Hill. 
The  quartzite  forms  the  eastern  slope  of  Maple  Hill  and  out- 
crops a  mile  eastward  at  the  apex  of  the  loop  formed  by  the 
road  that  runs  to  the  base  of  the  range,  east  of  Maple  Hill.  At 
the  latter  place,  within  a  space  of  50  feet,  the  structure  exhibited 
in  figure  28  was  shown.     The  quartzite  is  thin-bedded  and  lies 


Figure  28. — Structure  in  limestone  and  quartzite  east  of  Maple  Hill. 

quite  flat.  At  the  west  it  bends  downward  and  passes  beneath 
limestone  which  is  folded  down  at  a  rather  sharp  angle. 

North  of  Maple  Hill,  south  of  the  loop  road,  in  the  thick 
woods  on  the  north  side  of  a  deep  gully,  the  quartzite  in  vertical 
section  shows  the  structure  exhibited  in  figure  29.  The  folding 
of  the  quartzite  here,  as  contrasted  with  its  flat  position  farther 
south,  is  in  line  with  the  relations  exhibited  in  the  "Cobbles"  west 
of  Maple  Hill,  which  will  be  described  presently. 

Along  the  road  leading  to  the  old  abandoned  hamlet  of  Fay- 
ville  (see  Equinox  sheet;  not  shown  on  the  map  of  this  report) 


PLATE  LXIX. 


A.      BUCK'S  COBBLE,  A  VIEW  LOOKING  NORTH. 


B.      FOLD  IN  INTERBEDDED  QUARTZITE  ON  TRUMBULL  MT.  ON  THE 
CREST   OP  AN   OVERTURNED  ANTICLINE. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 


355 


quartzite  outcrops  in  the  bed  of  the  brook.  It  is  a  heavy,  com- 
pact rock  in  beds  from  2  to  5  feet  thick  and  strikes  N.  25°  W. 
with  a  dip  about  12°  S.  W. 

It  will  thus  be  seen  that  a  band  of  quartzite  2  miles  wide 
extends  north  from  Bennington  as  far  as  the  crossroad  from 
South  Shaftsbury  to  the  Madison  School.  So  far  as  observed, 
there  is  no  limestone  overlying  or  interbedded  with  the  quartzite, 
within  this  distance,  except  at  the  south  near  Bennington.  Along 
the  road  leading  northeast  from  the  covered  bridge  at  the  Mount 
Anthony  Golf  Club  links,  a  half  mile  north  of  the  railroad,  lime- 
stone outcrops  in  the  road  and  in  the  fields  east  of  it  are  numerous 
ledges.  A  reading  gave  the  strike  as  N.  13°  W.  and  a  dip  9°  west- 
erly. Because  of  their  apparent  superjacent  conformity  to  the 
quartzite  and  because  of  the  resemblance  to  other  limestone,  which 
the  writer  has  elsewhere  observed  in  the  Taconic  belt,  lying  a  little 
way  above  the  quartzite,  the  rock  was  closely  searched  for  Lower 
Cambrian  fossils,  but  without  success.  How  extensive  this  lime- 
stone is  north  and  east  of  these  outcrops  it  was  not  possible  to 
tell  on  account  of  the  drift.  Southward  from  them  there  are  no 
outcrops  in  Bennington  north  of  Main  St.,  so  far  as  observed. 
These  ledges  probably  represent  an  outlier  resting  on  the  quartz- 
ite and  conformable  with  it. 

The  sudden  transition  from  quartzite,  east  of  Buck's  Corner 
on  the  South  Shaftsbury  crossroad  to  the  limestone  of  Buck's 
Cobble  on  the  north  of  it  suggests  a  cross  fault  between  them. 
The  high  scarp  on  the  west  of  the  Cobble  suggests  a  strike  fault 
here,  which  extends  north  on  the  left  of  Harrington  Cobble, 
beyond  which  it  apparently  shortly  dies  out.  Harrington  Cobble 
has  much  the  same  structural  outlines  as  Buck's  Cobble  (see 
Plate  LXIX,  A)  but  its  western  slope  is  less  precipitous  and 
merges  gradually  into  the  eastern  slope  of  Hale  Mountain  at  the 
west.  The  western  slope  of  Hale  Mountain  is,  however,  deci- 
dedly steep  and  scarp-like.  The  limestone  on  the  east  slope  of 
Buck's  and  Harrington  Cobbles  dips  eastward  at  a  rather  high 
angle.  On  Hale  Mountain  a  reading  on  the  eastern  slope  at  the 
southern  end  gave  strike  N.  19°  E.,  dip  40°  E.,  and  on  the  north- 
ern slope,  strike  N.  46°  E.,  dip  23°  E. 


Figure  29.— Quartzite  north  of  Maple  Hill. 

As  contrasted  with  the  hills  at  the  north,  now  to  be  de- 
scribed, the  hmestones  of  Buck's  and  Harrington  Cobbles  and  of 


356  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Hale  Mountain,  so  far  as  observed,  show  no  associated  quartzite. 

At  Maple  Hill,  the  limestone  which  forms  the  summit  and 
western  slopes  exhibits  in  cross  section  a  close  folding  and  slight 
overturning  which  are  features  in  line  with  the  folding  of  the 
quartzite  (as  shown  in  figure  29)  at  the  northeastern  end  of  the 
hill.  Near  the  base  of  the  western  slope  the  rock  is  a  slightly 
banded,  rusty,  medium-grained  "buckwheat"  marble.  It  dips 
eastward  at  a  high  angle. 

The  hill  just  west  across  the  road  from  Maple  Hill  is  lime- 
stone. On  the  eastern  slope  the  beds  dip  eastward.  In  this 
hill  there  is  no  associated  quartzite.  Its  western  slope  is  steep 
and  suggests  a  break  as  also  does  the  slope  on  the  west  of  Maple 
Hill.     (See  Plate  LXIX,  B). 

The  next  hill  to  the  west  shows  quartzite  on  the  eastern  slope 
dipping  eastward,  but  at  the  summit  the  dip  is  westward,  in- 
dicating overturning.  My  notes  indicate  that  it  is  interbedded 
with  limestone  and  calcareous  quartzite. 

The  next  hill  on  the  west  is  Trumbull  Mountain.  At  the 
south  end  of  this  hill,  which  rises  very  steeply  from  the  road 
which  skirts  it  on  the  south,  the  quartzite  forms  the  eastern  slope, 
dipping  east.  Near  the  top  of  the  hill,  but  300  or  400  yards  east 
from  the  summit  of  the  western  slope,  quartzite  shows  a  struc- 
ture seen  in  Plate  LXX,  A,  which  is  a  view  looking  north.  It 
will  be  observed  that  the  bed  of  quartzite  dips  east  on  the  right 
of  the  photograph  and  west  on  the  left.  Associated  limestone 
beds  outcrop  near  by  at  the  south  on  the  southern  pitch  of  the  hill, 
also  dipping  slightly  west.  A  little  farther  west  they  stand 
nearly  vertical  and  on  the  western  slope  dip  to  the  east,  forming 
an  overturned  anticline. 

Similar  relations  were  shown  in  the  hill  east  of  Shaftsbury 
one  mile  north.  (See  Equinox  sheet).  Quartzite  which  forms  the 
eastern  slope  of  this  hill  outcrops  at  the  western  base  of  the  next 
hill  to  the  east  with  strike  N.  25°  E.  and  dip  of  24°  easterly. 


Figure    30. — Structure    seen    in    hill    near .  Shaftsbury,    interbedded    limestone 

and   quartzite. 

A  wide  swampy  track  borders  the  steep  western  scarp  of 
Trumbull  Mountain.  West  of  the  northward  extension  of  this 
swamp,  east-southeast  of  Shaftsbury  (see  Equinox  sheet),  is 
another  high  hill,  showing  interbedded  limestone  and  quartzite, 
standing  at  high  angles  on  the  summit.  At  one  place  the  struc- 
ture was  similar  to  the  accompanying  figure  30.     On  the  top  of 


PLATE  LXX. 


A.     LOOKING     NORTH     FROM     HARRINGTON     COBBLE.       TRUMBULL 
MOUNTAIN   ON  THE  LEFT.    .  MAPLE   HILL   ON   THE   RIGHT. 


MINOR    COMPRESSED    FOLDS    IN    LIMESTONE    OVERTURNED    TO 
THE  WEST,  ONE-HALF  MILE  NORTH  OF  HARRINGTON  COBBLE. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  357 

the  hill  the  limestone  was  folded  down  in  a  minor  syndinal.  The 
structure  was  interpreted  as  that  of  an  anticline,  but  with  one  or 
more  infoldings  along  its  crest. 

South  of  the  transverse  series  of  hills  beginning  with  Maple 
Hill  on  the  east  and  ending  with  Trumbull  Mountain,  between 
them  and  Harrington  Cobble  and  Hale  Mountain  at  the  south,  is 
a  gentle  westward  slope  of  low  rehef.  Plate  LXX,  A,  is  a  view 
looking  north  from  the  summit  of  Harrington  Cobble  across  this 
slope.  The  scarp-like  character  of  the  western  slopes  of  the  hills 
in  the  distance  is  brought  out  in  the  photograph.  The  lOO-foot  con- 
tours of  the  map  of  this  report  do  not  bring  out  these  hills  as' 
sharply  as  do  the  20-foot  contours  of  the  United  States  topographic 
sheet.  In  the  foreground  of  the  plate  is  the  gentle,  northern 
drift-covered  slope  of  Harrington  Cobble.  The  northern  slope 
of  Hale  Mountain  is  more  abrupt.  In  the  southern  portion  of 
the  gentle  western  slope,  north  of  the  crossroad  on  the  north  of 
Harrington  Cobble,  are  numerous  ledges  of  limestone.  In  the 
brook  that  crosses  this  portion  of  the  slope  the  limestone  dips 
gently  westward.  Plate  LXX,  B,  gives  a  view  of  a  portion  of  a 
limestone  ledge  500  or  600  yards  south  of  the  brook.  This  ledge 
was  interpreted  as  connecting  under  the  drift  with  Harrington 
Cobble  and  as  genetically  a  part  of  it,  thus  revealing  the  close- 
overturned  folding  that  caused  the  Cobble. 

The  general  flat  position  of  the  quartzite  in  the  broad  band 
north  of  Bennington  indicates  that  it  was  not  folded  much.  It 
buckled  a  httle.  In  its  southern  portion  a  downward  fold  caught 
and  preserved  the  hmestone  outlier  north  of  Bennington.  At 
the  northern  end  an  upward  bulge  formed  the  long  high  hill  of 
quartzite  south  of  Buck's  Cobble. 

All  the  different  hills  that  have  been  described  in  the  eastern 
part  of  Shaftsbury  are  of  similar  genetic  type,  including  the  hill 
of  quartzite  south  of  Buck's  Cobble.  They  form  long  camel- 
hump  arches  along  the  strike  with  anticlinal  structure  and  all  are 
overturned.  Probably  all  have  suffered  some  overthrusting  or 
developed  a  strong  tendency  in  that  direction.  It  may  be  that 
Buck's  and  Harrington  Cobbles  and  Hale  Mountain  had  a  quartz- 
ite member  of  the  interbedded  series  at  one  time  covering  them, 
but  not  being  so  violently  folded  as  the  hills  farther  north,  there 
was  no  infolding  of  the  quartzite  along  their  crests.  It  is  also 
possible  that  the  limestone  of  these  Cobbles  belongs  to  a  higher 
horizon  than  the  interbedded  limestones  and  quartzites  farther 
north  and  that  the  latter  did  not  reach  the  surface  in  Buck's  and 
Harrington  Cobbles.  The  former  view,  however,  seems  more 
likely  because  the  limestone  outlier  north  of  Bennington  would 
seem  to  suggest  that  the  quartzite  was  succeeded  by  a  certain 
thickness  of  limestone  before  the  deposition  of  the  interbedded 
series  and  the  occurrence  of  the  quartzite  at  the  surface  at  the 
south  points  to  diminishing  reversed  faulting  northward  so  that 


358  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Buck's  and  Harrington  Cobbles  with  Hale  Mountain  take  an  in- 
termediate position  with  respect  to  the  quartzite  south  of  them 
and  the  interbedded  series  at  the  north.  The  exact  relation  of 
the  broad  quartzite  band  to  the  adjacent  limestone  on  the  west 
could  not  be  positively  determined,  but  I  believe  it  is  a  faulted 
one.  An  intersecting  cross  fault  south  of  Buck's  Cobble  dies 
away  eastward.  North  of  this  break  folding  was  more  violent, 
the  tendency  towards  which  is  recorded  in  the  quartzite  at  the 
high  hill  just  south  of  Buck's  Cobble.  The  tendency  to  folding 
increased  northward  and  inversely  as  the  tendency  to  upthrust  of 
the  lower  beds  diminished. 

If  there  is  a  reversed  fault  on  the  west  of  the  broad  band 
of  quartzite  it  becomes  a  question  how  far  north  it  should  be 
drawn.  The  interbedded  series  appear  to  be  at  no  great  distance 
above  the  basal  quartzite,  whether  we  reason  from  the  surface 
succession  northward  from  Bennington  or  eastward  from  the 
range  through  Maple  Hill,  and  I  have  drawn  a  probable  break 
northward  to  the  limit  of  the  map  to  show  the  probable  close  age 
relation  of  all  the  rocks  of  this  broad  band  on  the  east  of  the 
valley  north  of  Bennington  with  intervening  probable  strike  faults 
between  this  major  break  and  the  foot  of  the  range. 

In  view  of  the  heavy  drift  covering  in  the  central  and  west- 
ern part  of  Shaftsbury  the  probable  stratigraphical  relations  of 
the  east  and  west  portions  of  the  valley  in  this  town  are  hard 
to  work  out.  If  there  is  a  reversed  fault  all  along  the  western 
edge  of  the  quartzite  and  the  series  of  "Cobbles"  north  of  it,  it 
would  mean  that  the  interbedded  series  underwent  some  folding 
before  the  break  occurred  and  were  caught  at  whatever  stage  of 
folding  they  had  attained  when  the  heavy  quartzite  basal  member 
broke. 

South  of  Bennington  the  interbedded  series  lies  flat  for  the 
most  part.  The  high  hill  just  west  of  the  brook  that  joins  South 
Stream  three-fourths  of  a  mile  northwest  of  the  old  lumber  mill 
shows  interbedded  calcareous  quartzite  and  limestone  like  those 
in  the  hills  of  Shaftsbury  and  obeys  a  similar  arching  tendency 
along  the  strike.  A  reading  on  the  steep  eastern  slope  of  this  hill 
gave  the  strike  as  N.  35°  E.  and  the  dip  80°  E.  At  the  northern 
end  of  the  hill  a  reading  gave  strike  N.  33°  E.  and  dip  70°  W. 

Placing  this  hill  with  the  valley  quartzite  formation  the 
western  boundary  of  the  latter  should  perhaps  be  drawn  through 
or  on  the  west  of  this  hill  and  southward  so  as  to  include  the 
spur  sticking  out  northwest  from  the  range  towards  Barber's 
Pond.  The  limestone  of  the  base  of  this  spur  in  its  lithology 
recalls  the  limestone  of  the  outlier  north  of  Bennington  and 
underlies  the  interbedded  upper  series  of  the  spur. 

Possibly  the  western  margin  should  be  drawn  even  farther 
west  to  include  certain  outcrops  south  of  Meyer's  house  on  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  359 

extreme  northeastern  slope  of  Mason  Hill  which  are  lithologically 
similar  to  the  limestones  just  mentioned. 

The  calcareous  quartzites  of  the  interbedded  series  so 
strongly  resemble  the  quartzite  that  one  must  always  carefully 
examine  them  to  be  sure.  They  weather  to  look  like  the  quartzite 
although  frequently  showing  a  pitted  surface.  These  siliceous 
limestones,  as  they  may  be  equally  well  designated,  effervesce 
rather  strongly  with  cold  dilute  acid  and  under  the  microscope 
show  an  approximately  equivalent  amount  of  calcite  and  quartz 
distributed  in  grains  over  the  section  in  such  manner  as  to  in- 
dicate detrital  origin  for  both  and  free  admixture  during  deposi- 
tion. The  siliceous  elements  of  the  thin  section  show  some 
microcline  and  other  feldspar  but  are  predominately  quartz. 

THE  LIMESTONE  FORMATION  IN  AND  SOUTH  OF 
BENNINGTON. 

On  Hillside  street  in  Bennington,  near  the  house  of  J.  T. 
Remington,  the  limestone  as  blasted  in  the  road  shows  the  struc- 
ture as  exhibited  in  figure  31.  The  section  indicates  close  fold- 
ing, overturning  and  reversed  faulting. 


Figure  31. — Limestone  on  Hillside  Street,  Bennington,  near  J.  T.  Remington's. 

Just  south  of  Main  street  under  the  west  bank  of  the 
cemetery  the  limestone  dips  easterly  at  54°  and  strikes  N.  31°  E. 
One  mile  south  of  Main  street,  along  the  road  leaving  the  latter 
west  of  Jewett  Brook,  near  "Camp  corner,"  in  the  quarry  beside 
the  road,  the  limestone  dips  60-65°  easterly,  the  strike  in  the 
quarry  varying  in  a  distance  of  50  feet  from  N.  45°  W.  to  N. 
7°  W.  One-half  mile  directly  south  of  this  quarry,  on  the  north- 
ern slope  of  the  hill,  the  limestone  lies  quite  flat.  This  outcrop 
is  on  the  extreme  northwestern  slope  of  the  hill  which  a  mile  to 
the  southeast  shows  interbedded  limestone  and  calcareous  quartz- 
ite as  described  above,  dipping  80°  E.  on  the  eastern  slope  and 
70°  W.  on  the  northern  slope. 

In  Bennington  on  Main  street  near  the  mill  pond  the  lime- 
stone dips  eastward  at  a  low  angle  and  shows  shearing  structure 
dipping  eastward  at  a  high  angle. 

South  of  Bennington,  between  South  street  and  Dunham 
avenue  and  the  Pownal  road,  the  limestone  is  dove-colored,  carry- 
ing many  wavy  bands  of  a  chamois  color,  reminding  the  writer 
very  strongly  of  certain  portions  of  the  calciferous  of  Dutchess 


360  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

County,  N.  Y.  The  rock  has  every  appearance  of  having  under- 
gone shearing  whch  has  developed  an  eastward  dip  so  that  it 
proved  very  difficult  to  distinguish  between  shearing  and  bedding. 
Near  the  Pownal  road  the  dove  and  buff  seem  to  be  clearly  inter- 
bedded,  dipping  east  so  that  the  shearing  is  with  the  bedding,  but 
200  yards  to  the  southwest  the  dip  is  19°  W.  with  the  strike  of 
N.  27°  W.  Weathered  surfaces  were  searched  for  fossils  with- 
out success.  It  was  not  possible  from  the  surface  exposures 
to  determine  to  what  extent  the  shearing  and  dip  approximately 
coincided. 

In  Bennington,  three-fourths  of  a  mile  west  of  South  street, 
in  the  Lebanon  Springs  R.  R.  cut  the  limestone  dips  east  with 
shearing  joints  across  the  bedding. 

In  the  field  north  of  Dunham  avenue,  between  it  and  the  next 
road  north,  a  greatly  brecciated  limestone  appears  in  numerous 
small  and  large  ledges  over  an  area  several  acres  in  extent. 
Plate  LXXI  shows  the  vertical  face  of  one  of  these  ledges.  The 
brecciation  is  often  coarser  than  that  shown  in  the  plate,  but  is 
also  rather  fine,  the  two  passing  into  one  another.  The  frag- 
ments range  from  the  size  of  a  marble  to  that  of  a  man's  head. 
The  brecciation  is  clearly  apparent  on  the  lichen-covered  surface 
outcrops  but  is  most  conspicuous  on  comparatively  fresh  surfaces. 

Just  west  of  the  Pownal  road,  a  few  hundred  yards  north- 
west of  these  brecciated  outcrops,  the  limestone  strikes  N.  81°  W. 
and  dips  24°  southerly. 

Both  east  and  west  of  the  Pownal  road,  south  of  Robinson's 
crossroads,  and  one  mile  north-northeast  of  Carpenter  Hill,  the 
limestone  generally  dips  westward.  One  reading  one-half  mile 
south  of  the  crossroads  gave  the  strike  N.  30°  W.  and  dipped 
48°  westerly.  At  this  place  there  is  confusion ;  .another  reading 
gave  a  dip  clearly  to  the  southeast.  The  limestone  is  frequently 
brecciated,  breaking  into  many  irregular  pieces  under  the  hammer. 
Westward  up  the  hill  the  dip  is  eastward. 

Along  the  mountain  road,  running  west  of  Carpenter  Hill, 
about  a  mile  and  a  fourth  from  Robinson's  crossroad,  and  just 
beneath  the  eastern  edge  of  the  Mount  Anthony  schist,  which 
rises  very  steeply  here,  the  structure  shown  is  exhibited  in  the 
composite  section  of  figure  32.  One-fourth  of  a  mile  northeast 
of  this  outcrop,  just  west  of  the  road,  the  limestone  shows  pro- 
nounced shearing.  It  is  the  gray  or  dove-colored  rock  seen  so 
frequently  farther  north,  to  the  east  of  the  Pownal  road,  and 
carries  the  same  chamois-colored  wavy  patches  and  streaks. 

Just  south  of  the  ledge,  whose  structure  is  shown  in  figure 
32,  the  limestone  of  Carpenter  Hill  gives  place  to  schist.  On  the 
summit  of  this  hill  the  eastern  margin  of  the  schist  is  one-half 
mile  farther  east  than  along  the  mountain  road.  In  both  places 
the  schist  dips  to  the  west. 


PLATE  LXXI. 


A    LEDGE    OP    COARSELY    BRECCIATED    LIMESTONE    WEST    OF 
DUNHAM  AVENUE  IN  BENNINGTON. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


361 


Existing  maps  show  the  limestone  passing  over  the  moun- 
tain west  of  Carpenter  Hill  to  join  the  limestone  in  the  valley  of 
the  Hoosick.  My  observations  find  the  schist  intervening  and  con- 
tradict this  connection  across  the  mountain. 

The  limestone  east  of  Carpenter  Hill  and  southward,  west 
of  the  Pownal  road  along  the  foot  of  the  mountain  to  Pownal 
Center,  so  far  as  observed,  dips  westward  beneath  the  schist. 
Where  Jewett  Brook  crosses  the  road,  and  in  the  electric  rail- 
way cut  just  east,  the  dip  is  apparently  eastward. 


PiGUEE  32. — 10'-12'  Limestone  and  schist  on  east  side  of  Mount  Antliony,  near 
Carpenter   Hill.     Composite   section. 

Only  a  few  non-committal  outcrops  occur  southeastward  on 
the  hills  as  far  south  as  the  road  going  east  from  Pownal  Center. 
On  the  northeastern  slope  of  the  hill  lying  in  the  angle  between  this 
road  and  the  one  going  south  from  "Irish  corner"  the  limestone 
and  schist  are  mixed  in  great  confusion,  outcrops  of  one  passing 
within  short  distances  into  those  of  the  other,  the  whole  side  hill 
presenting  the  aspect  of  limestone  overthrust  or  overfolded  and 
resting  on  the  schist. 

Around  Barber  Pond  and  northward  for  a  distance  of  three 
miles  or  more  the  drift  conceals  the  limestone,  leaving  the  struc- 
ture over  this  broad  area  wholly  in  the  dark. 

It  is  a  problem  how  to  interpret  the  structure  of  the  lime- 
stone south  of  Bennington,  but  the  observations  which  have  been 
noted  show  close  folding,  overturning,  overthrusting,  extreme 
and  violent  brecciation  and  shearing.  I  believe  the  limestones 
south  of  Bennington  to  be  mainly  older  than  those  which -pass 
beneath  the  schist  of  Mount  Anthony.  Studies  which  the  writer 
has  elsewhere  made  in  the  Taconic  rocks  have  shown  great  blocks 
of  limestone  to  move  upward  as  a  mass  by  reverse  faulting 
against  younger  strata,  at  the  same  time  suffering  extreme  fold- 
ing and  minor  breaks  within  the  block. 

I  would  hesitate  to  assert  that  this  is  what  has  happened 
south  of  Bennington,  but  in  view  of  the  tendency  to  reverse  fault- 
ing and  the  structural  features  observed  in  the  field  such  a  history 
does  not  appear  improbable. 


362  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

LIMESTONE  AND  SCHIST  NORTHWEST  OF 
BENNINGTON. 

Limestone  outcrops  in  the  road  and  along  the  Walloomsac 
in  Papermill  Village  and  in  Paran  Creek  along  the  trolley  road 
toward  North  Bennington.  Outcrops  in  Papermill  Village  show 
some  minor  folding  westward.  In  the  quarry  east  of  the  lumber 
mill  on  Paran  Creek  and  a  few  hundred  yards  south  of  it  the 
strike  is  N.  80°  E.  and  the  dip  11°  S.  SE.  The  fiat  position  of 
the  limestone  in  the  bed  and  eastern  bank  of  the  creek,  south  of 
North  Bennington,  is  very  conspicuous. 

North  of  the  village  the  limestone  outcrops  in  patches  here 
and  there.  One  of  these  is  at  Mattison  corner  and  others  occur 
a  mile  to  the  north  in  the  fields  southeast  of  Horton  corner. 
Along  the  eastern  slope  of  the  hill  at  the  latter  locality  the  dip  is 
west-northwest  at  one  place  and  at  another  apparently  northeast, 
forming  a  part  of  a  low  doming  arch. 

Abundant  outcrops  occur  in  the  fields  west  and  northwest 
of  Morton's  corner  near  "Cold  Spring."  A  reading  of  the  dip 
gave  14°  NW.  North  of  Clark's  corner  another  reading  gave 
the  apparent  dip  southeast  at  a  high  angle,  but  at  this  place  the 
rock  was  greatly  sheared  and  distinction  between  dip  and  shearing 
was  not  easily  made.  A  patch  of  the  limestone  north  of  "Cold 
Spring"  showed  many  gray  patches  resembling  fossils  on  the 
weathered  surface.  Nothing  positively  distinct  was  found  and 
the  rock  was  too  tough  to  break. 

The  limestone  formation  over  much  of  the  area  north  of 
Bennington  shows  the  same  gray  rock  which  streaks  and  patches 
of  bufif  as  described  for  so  much  of  the  area  south  of  Bennington, 
and  likewise  showed  evidence  of  much  shearing. 

On  the  west  slope  of  the  hill  at  Taper's  corner,  one  and  a  half 
miles  south  of  Shaftsbury  Center,  the  limestone  dips  to  the  north. 
In  the  Rutland  R.  R.  cut  a  mile  northeast  of  South  Shaftsbury 
the  dip  is  to  the  south.  Southeast  of  South  Shaftsbury  the  dip 
is  south  or  southeast. 

On  the  southeastern  slope  of  West  Mountain  the  schist  comes 
down  to  within  a  half  mile  of  the  Shaftsbury  road.  The  south- 
ernmost outcrops  of  limestone  just  north  of  the  road  running 
west  of  Shaftsbury  Center  dip  to  the  south.  Along  the  base  of 
the  eastern  slope  of  the  mountain  one-half  mile  farther  north  the 
dip  could  not  be  made  out. 

There  is  seen  to  be  considerable  apparent  variation  in  the 
strike  and  dip  of  the  limestone  formation  north  of  North  Ben- 
nington. In  some  cases  the  dip  may  have  been  that  of  shearing 
structure,  but  in  general  the  limestone  appears  to  lie  in  gentle 
undulating  folds  and  to  have  suffered  shearing  which  has  pro- 
duced an  apparent  eastward  dip  in  many  cases. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  363 

North  of  the  road  at  the  base  of  the  southern  slope  of  _ West 
Mountain  the  schist  formation  succeeds  the  limestone  dipping  to 
the  east-southeast. 

In  North  Bennington  village,  one-half  mile  northwest  of 
the  post  office,  near  the  railroad  track,  slate  or  phyllite  outcrops 
dipping  west  with  eastward  cleavage.  A  few  hundred  _  yards 
west  are  outcrops  of  limestone.  Westward  in  the  direction  of 
Sodom  the  limestone  gives  place  to  slates. 

The  eastern  and  southern  slopes  of  the  low  hill  southwest 
of  Bennington  are  underlain  by  limestone  dipping  to  the  south- 
east. This  limestone  is  farther  west  than  the  slate  in  North 
Bennington  village.  On  the  western  slope  of  the  hill  the  lime- 
stone is  succeeded  by  papery  slates  which  are  the  southward  con- 
tinuation of  the  outcrops  at  Sodom. 

On  the  south  slope  of  the  hill  the  limestone  comes  down  close 
to  Henry  Bridge  and  continues  across  the  Walloomsac.  A  half- 
mile  southwest  of  the  bridge  the  papery  slates  outcrop  in  the 
brook  on  the  west  side  of  the  road  dipping  to  the  southwest  with 
strike  N.  55°  W.  The  limestone  occurs  a  few  yards  east  on  the 
east  side  of  the  road.  On  the  east  slope  of  the  hill  to  the  south- 
west of  these  outcrops  the  limestone  rests  on  the  slate. 

The  high  hill  southeast  of  the  "ore  pit"  is  capped  by  slates 
and  flanked  by  limestone  on  the  east. 

The  schist  was  thus  traced  along  an  irregular  line  beginning 
two  miles  west  of  the  northern  end  of  Mount  Anthony,  as  shown 
on  the  map,  as  far  north  as  Sodom.  Another  trip  was  planned 
to  trace  the  boundary  north  from  Sodom.  There  are  reasons  for 
thinking  that  the  Vermont  Report  has  the  boundary  substantially 
correct  in  representing  the  limestone  as  entirely  cut  off  in  the 
west  by  the  slate  just  east  of  the  state  boundary. 

The  apparent  dip  of  the  schist  up  the  south  slope  and  at  the 
summit  of  West  Mountain  is  eastward.  The  rock  at  the  summit 
is  a  sericite  schist  which  does  not  differ  essentially  from  that  of 
Mann  Hill  both  in  the  hand  specimen  and  in  thin  section. 

The  country  immediately  southeast,  east  and  northeast  of 
North  Bennington  and  northward  through  South  Shaftsbury  and 
Shaftsbury  Center  is  so  largely  drift  covered  that  outcrops  are 
few  and  to  a  great  extent  non-committal.  Limestone  outcrops  on 
the  west  slope,  southeast  of  South  Shaftsbury,  below  the  slope 
that  truncates  the  beds  of  the  quartzite,  with  strike  N.  40°  E. 
and  dip  of  18°  E.  The  limestone  outcrops  at  a  few  places  in 
the  Rutland  R.  R.  cut  north  of  South  Shaftsbury. 

The  outcrops  on  the  whole  through  this  drift-covered  area 
suggest  that  the  limestone  is  not  greatly  folded,  as  is  also  the  case 
around  North  Bennington. 

The  western  portion  of  this  broad  valley  area  northwest  of 
Bennington  is  much  sheared  and  the  field  observations  indicate 
that  the  limestone  has  been  pushed  against  and  over  the  schist 


364  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

at  the  west.  The  map  shows  that  this  hmestone  area  has  suffered 
at  offset  to  the  west  corresponding  with  that  in  the  valley  quartz- 
ite  north  of  Bennington  and  also  with  that  of  the  Bald  Mountain 
mass. 

Throughout  this  broad  area  no  marbles  were  found  corre- 
sponding with  those  that  pass  beneath  Mount  Anthony  and  the 
formation  was  considered  to  belong  to  an  older  terrane  than  the 
Mount  Anthony  limestone. 

It  was  hardly  possible  to  make  out  the  structural  relations 
on  the  south  and  east  of  West  Mountain.  The  schist  of  West 
Mountain  is  regarded  as  younger  than  the  limestone  and  so  also  is 
that  which  the  valley  limestone  rests  against  or  upon  at  the  west. 

It  is  not  possible  to  assert  how  far  west  the  great  fault  that 
bounds  Bald  Mountain  on  the  south  extends  in  the  limestone 
northwest  of  Bennington  and  so  it  is  represented  as  dying  away 
west  of  Bennington. 

LIMESTONE  AND  SCHIST  OF  MT.  ANTHONY  SOUTH- 
WEST AND  WEST  OF  BENNINGTON. 

Beginning  at  a  point  about  three  miles  south  of  Bennington 
Center  near  the  base  of  the  eastern  slope  of  Mt.  Anthony  and 
proceeding  northward  along  the  slope,  the  limestone  was  found 
dipping  westward  into  the  mountain  beneath  the  schist.  The 
formation  is  sometimes  thinly  bedded,  but  consists  mainly  of  beds 
of  white  or  clouded  marble  ranging  from  two  to  three  or  more 
feet  in  thickness.  The  dip  is  as  low  as  5°  in  some  places  and 
always  at  a  low  or  moderate  angle.  Towards  the  northern  end 
of  the  mountain  the  dip  changes  to  the  southwest  and  at  the  north- 
ern end  to  due  south.  Southwest  of  Dunham's  corner  the  lime- 
stone shows  much  confusion  of  strike  and  dip,  the  latter  changing 
from  easterly  dip  through  a  vertical  position  to  the  characteristic 
southwest  dip.  The  schist  near  here  is  two  or  three  hundred 
feet  below  its  normal  contour.  A  small  normal  fault  has  dropped 
the  schist  and  disturbed  the  limestone. 

In  quarry  excavations  just  southeast  of  the  Edward  H. 
Everett  mansion  the  strike  of  the  limestone  was  N.  29°  W.  with 
dip  28°  S.  W.  Along  the  wood  road  following  up  the  brook  west 
of  the  mansion  the  slaty  schist  appears  showing  eastward  dip- 
ping cleavage.  The  limestone  outcrops  a  few  yards  north  on 
nearly  the  same  contour.  Farther  up  the  mountain  in  the  woods 
at  an  old  quarry  the  schist  rests  conformably  on  blue  limestone 
which  strikes  N.  80°  W.  and  dips  47°  southerly. 

Along  the  edge  of  the  woods  northwest  of  the  Everett  man- 
sion the  limestone  varies  in  strike  between  due  east  and  west  and 
N.  48°  W.  Along  the  northwestern  slope  a  short  distance  up 
from  the  base  the  rock  is  a  thick-bedded  marble.  Along  the 
northern  slope  just  below  the  woods  these  heavy  beds  dip  south- 


PLATE    LXXIT. 


BLUE  CRYSTALLINE  LIMESTONE  BENEATH  MT.  ANTHONY 
SCHIST  AT  COLGATE'S  QUARRY.  THE  ROCK  IS  USED  FOR  ROAD 
METAL. 


-^gSoa^j^"  •  '^.^'■s-a;. 


B.       CONFORMABLE   SCHIST  AND  LIMESTONE  JUST  SOUTH  OF  OUT- 
CROP  IN  PLATE   VI. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  365 

ward  and  this  same  dip  appears  along  the  Pownal  road  from 
Bennington  Center  just  west  of  the  brecciated  ledges  which  were 
described  above  and  also  along  the  road  running  east  and  west 
through  Bennington  Center. 

A  private  road  ascends  the  northwest  slope  of  Mount  An- 
thony on  the  estate  of  James  C.  Colgate.  Along  this  road  the 
limestone  gives  place  to  the  schist  which  strikes  N.  50°  E.  and 
dips  20°  easterly.  In  some  slaty  beds  in  this  schist  some  distance 
up  the  road  a  crushed  crinoid  stem  was  found. 

Along  the  road  to  North  Pownal,  which  branches  from  the 
Bennington-Hoosick  road  on  the  west  side  of  Mount  Anthony, 
the  dip  of  the  limestone  is  southerly.  In  a  quarry  used  for  road 
metal,  about  a  mile  south  of  the  Bennington-Hoosick  road,  a  blue 
limestone  with  the  same  southerly  dip  conformably  underlies  the 
schist  (see  Plates  LXXII,  A,  and  LXXII,  B).  The  conditions  are 
similar  to  those  in  the  quarry  in  the  woods  west  of  the  Everett 
mansion. 

In  Bennington  Center,  three-fourths  of  a  mile  northwest 
of  the  monument,  the  limestone  was  observed  with  the  same 
southerly  dip. 

Along  the  North  Pownal  road,  from  the  quarry  south  of  Col- 
gate, only  the  schist  formation  outcrops  to  within  a  mile  of 
North  Pownal  village.  The  western  slope  of  Mount  Anthony  is 
schist  and  this  was  followed  over  the  ridge  to  Carpenter  Hill.  If, 
as  seems  likely,  there  is  a  fault  on  the  northwest  of  Mount  An- 
thony it  dies  away  southward. 

Mount  Anthony  is  a  synclinal  pitching  southward  and  capped 
by  the  schist  formation  which  is  conformably  underlain  by  blue 
crystalline  limestone  and  heavy-bedded  marble  which  outcrop  on 
the  northwest,  north,  northeast  and  a  part  of  the  east  slopes 
of  the  mountain. 

THE  LIMESTONE  AND  SCHIST  IN  NORTH  POWNAL 
AND  POWNAL  VILLAGES. 

Northeast  and  east  of  North  Pownal  village  is  a  large  inlier 
of  Hmestone,  as  shown  on  the  map.  It  extends  east  of  North 
Pownal  as  far  as  the  road  running  south  from  Arnold's  (school 
house)  corner  along  which  it  is  mixed  with  the  slate  as  far  as 
the  next  corner  south.  This  inlier  is  surrounded  by  the  slate  or 
schist  on  the  west,  north  and  east  and  at  the  south  extends  along 
the  valley  of  the  Hoosick  as  far  as  Pownal.  South  of  Pownal 
it  seems  to  be  cut  off  by  the  schist  from  the  limestone  northwest 
of  WilHamstown. 

At  the  northern  end  of  this  inlier,  east  of  the  road  from 
Bennington  Center  to  North  Pownal,  the  limestone  forms  a  con- 
spicuous hill.  A  reading  here  gave  the  strike  N.  35°  E.  and  the 
dip  23°  SE.     Across  the  road  at  the  "Wash  Tubs"   (see  plate 


366  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

LXXIII)  the  limestone  arches  gently  as  shown  in  figure  33.  At 
this  place  the  stream  has  cut  into  the  gently  arching  limestone  and 
made  a  series  of  large  pot-holes  locally  known  as  the  "Wash 
Tubs." 

In  the  old  quarry  at  Whipple's  corner  in  North  Pownal 
village  the  limestone  is  rather  massive.  In  the  north  wall  a  small 
overturned  fold  was  observed,  the  axial  plane  lying  flat.  In  the 
south  wall  the  dip  appeared  to  be  gently  westward,  but  dynamic 
movement  has  largely  effaced  distinct  bedding. 

East  of  Main  street  in  the  village  the  limestone  forms  a  high 
scarp  to  a  point  one-half  mile  south  of  the  railway  station.  At 
the  quarry  at  North  Pownal  station  the  limestone  shows  folding 
on  large  and  small  scales  with  severe  jamming.  In  the  railroad 
bank  just  under  the  highway,  southwest  of  the  quarry,  is  the  slate 
which  is  greatly  jammed  and  crushed.  Just  across  the  river 
opposite  the  quarry  the  slate  or  phyllite  forms  a  knoll  between 
the  river  and  the  road  near  the  Dean  place.  Here  the  slate  shows 
severe  crumpling  which  dips  eastward. 


Figure  33. — Limestone  structure  at  Wash  Tubs. 

Southward  along  the  west  bank  of  the  stream  a  thick  drift 
covering  conceals  the  rock  near  the  river,  but  schist  outcrops  up 
the  slope  of  the  hill  to  the  west.  A  mile  south  from  the  Greylock 
Mills,  on  the  west  side  of  the  stream,  a  knoll  of  limestone  lies 
close  to  the  river  clearly  resting  on  or  against  the  slates.  South 
of  this  outcrop  past  the  abandoned  Service  farmhouse  all  is  slate 
nearly  to  Daniel  Gardner's  house. 

Along  the  road  south  from  the  Service  house,  just  after  it 
makes  its  turn  west  of  Gardner's  house,  the  slate  outcrops  in  the 
road  and  the  brook  with  limestone  in  close  proximity.  The  actual 
contact  was  not  seen  but  the  two  are  less  than  eight  feet  apart. 
Limestone  outcrops  south  of  the  road  and  elsewhere  partly  sur- 
rounding the  slate,  indicating  that  the  limestone  has  been  pushed 
over  on  the  slate. 

At  the  bridge  in  Pownal  limestone  outcrops  in  the  bed  of 
the  river. 

Along  the  road  west  of  the  Hoosick,  south  of  Pownal,  the 
drift  hides  the  underlying  rock,  but  near  the  quadrangle  boundary, 
a  half  mile  east  of  the  road,  near  the  railroad  bridge,  the  schist 
outcrops  in  numerous  ledges  dipping  west  into  the  hill.  West- 
ward the  schist  passes  beneath  the  drift  of  an  immense  drumlin. 
It  forms  the  west  bank  of  the  river  south  of  the  railroad  bridge, 
but  east  of  the  river  is  succeeded  by  Hmestone. 


PLATE    LXXIIl. 


THE  WASH  TUBS,  NORTH  POWNAL. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  367 

In  thin  section  this  schist  shows  a  felt  work  of  sericite  with 
quartz  and  some  magnetite  as  accessory  and  numerous  flakes  of 
chlorite  rather  uniformly  distributed  in  the  section.  In  corre- 
spondence with  the  presence  of  the  latter  the  hand  specimen 
shows  a  greenish  color,  although  the  parting  planes  show  the 
same  silvery  luster  exhibited  by  the  schist  of  Mann  Hill. 

On  the  map,  between  the  railroad  bridge  and  Pownal,  the 
schist  of  Mason  Hill  is  made  continuous  with  that  west  of  the 
river.  The  schist  was  traced  along  the  Pownal  road  east  of  the 
Hoosick  to  and  through  the  village  of  Pownal  to  a  point  about  one 
mile  south  of  North  Pownal  station,  where  it  is  succeeded  by  the 
high  scarp  of  limestone  along  the  road.  At  this  point  the  bound- 
ary turns  northeastward  and  passes  west  of  the  brook  to  the 
mixed  outcrops  of  schist  and  limestone  that  have  been  described. 

All  along  the  Pownal  road  at  the  base  of  the  westerly  slope 
of  Mason  and  Mann  hills,  the  dip  of  the  schist  is  eastward, 
while  west  of  the  river,  so  far  as  observed,  it  is  normally  west- 
ward. 

The  eastern  margin  of  the  limestone  hill  east  of  North 
Pownal  shows  pronounced  shearing,  especially  about  one  mile 
north  of  Wright  Bridge  corner,  just  west  of  the  brook.  It  is 
here  a  gray  rock  with  chamois-colored  stringers  and  patches  like 
that  so  common  north  and  south  of  Bennington.  Although  the 
limestone  in  the  quarries  in  North  Pownal  is  somewhat  different, 
in  the  surface  outcrops  near  by,  it  weathers  in  a  similar  way.  I 
have  not  found  in  this  inlier  any  heavy  beds  of  marble  like  those  on 
the  east  and  north  slopes  of  Mount  Anthony. 

I  look  upon  this  limestone  at  North  Pownal  as  a  faulted  inlier 
which  is  thrust  against  or  on  the  slates  at  the  west  and  which 
pinches  out  southward  in  Pownal  village. 


SCHIST  OF  MANN  HILL. 

Through  the  fields  and  along  the  road  from  North  Pownal 
northeastward  to  Carpenter  Hill  and  eastward  to  Pownal  Center 
are  numerous  outcrops  of  the  schist  dipping  east.  Along  the 
eastern  margin  of  the  Mount  Anthony  ridge  north  of  Pownal 
Center  the  dip  is  westward  into  the  hill.  There  is,  therefore, 
Avithin  a  mile  going  south,  a  change  in  dip  from  west  to  east.  All 
the  schist  south  of  the  road  from  Pownal  Center  to  North  Pownal 
and  along  the  road,  as  described  above,  from  Pownal  to  North 
Pownal,  and  on  the  west  slope  and  summit  of  Mann  Hill  dips  east. 
On  the  east  slope  of  Mann  Hill  the  schist  also  dips  east  and  passes 
beneath  the  hmestone  which  is  mixed  with  the  schist  in  great 
confusion  south  of  "Irish  corner"  as  described  above. 

The  schist  of  Mann  Hill  has  been  overturned,  and  the  lime- 
stone east  of  it  has  been  either  thrust  or  overturned  on  it. 


368  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

The  rock  at  the  summit  of  Mann  Hill  is  a  silvery  sericite 
schist.  In  thin  section  it  shows  a  felt  work  of  sericite  with  quartz 
and  without  apparent  accessories. 

THE  SCHIST  AND  LIMESTONE  OF  MASON  HILL. 

The  summit  and  western  slope  of  Mason  Hill  are  underlain 
by  schist  similar  to  that  of  Mann  Hill.  Along  the  road  over  the 
summit  it  is  noticeably  crumpled. 

The  modified  drift  is  piled  high  against  the  southwestern 
slope  of  Mason  Hill  above  the  Hoosick  River.  Limestone  out- 
crops from  beneath  the  drift  along  the  Williamstown-Pownal 
road  a  hundred  yards  southeast  of  the  railroad  bridge. 

A  road  ascends  the  hill  one-fourth  of  a  mile  south  of  this 
outcrop.  Four  or  five  hundred  yards  north  of  this  road  just 
above  the  gravel  pits  limestone  lies  on  the  sericite  schist  as  shown 
in  figure   34.     The   limestone   continues   up   the   hill   northward 


if       y^ 

^^^ _    S...K.,,^ 

1^'     ™ 

y^               Slope  of  Mason  Hill 

/ 

e. 

Figure 

34.- 

— Limestone   and    schist. 

along  the  slope  and  is  succeeded  by  the  schist,  both  dipping  east- 
erly.    Here  again  the  limestone  rests  on  the  schist. 

East  of  the  road  over  Mason  Hill  the  schist  outcrops  under 
the  west  bank  of  Reservoir  Brook  and  just  across  the  brook  less 
than  50  feet  away  rises  the  high  scarp  of  compact,  white  quartzite. 
The  schist  along  Reservoir  Brook  is  greatly  shattered.  This 
broken  schist  was  also  found  east  of  Meyer's  house  along  the  road 
and  at  this  place  lies  close  to  the  northward  extension  of  the 
fault  along  Reservoir  Brook. 

Along  the  Pownal  road  towards  Williamstown  the  limestone 
outcrops  along  the  east  side  of  the  road  with  southeasterly  dip 
and  strike  N.  18°  E.,  and  southward  joins  the  limestone  area  of 
Williamstown. 

The  Hoosick  between  the  Massachusetts  line  and  North 
Pownal  has  apparently  availed  itself  of  a  great  line  of  rupture. 
Along  this  break  the  limestone  has  come  to  the  surface,  as  now 
exposed,  except  in  the  interval  between  Pownal  and  the  railroad 
bridge  two  miles  southeast  of  the  village  along  which  the  schist 
of  Mason  Hill  apparently  joins  that  west  of  the  river. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  369 

GENERAL  RELATIONS. 

It  is  difficult  to  represent  on  the  map  the  probable  intricate 
structural  relations  of  the  rocks  of  the  area.  The  writer  hoped 
by  another  season's  work  to  get  some"  light  on  the  relative  ages 
of  the  rocks  which  in  so  many  cases  apparently  lie  in  faulted 
positions  against  each  other. 

It  is  possible  that  the  major  flexures  which  ultimately  were 
to  find  expression  in  the  Green  Mountain  elevation  began  early 
in  the  Cambrian  period  and  that  folding  went  on  slowly  enough 
to  allow  for  continuous  deposition  from  Lower  Cambrian  to 
Ordovician.  The  writer  has  elsewhere  suggested  that  faulting 
and  erosion  may  possibly  account  for  the  apparent  absence  of 
portions  of  the  Cambrian. 

The  thick  masses  of  sediments  which  accumulated  in  the 
great  troughs  of  the  older  rocks  underwent  profound  folding  as 
the  basement  crystalline  floor  slowly  closed  in  on  them.  They 
were  often  greatly  jammed,  overturned  and  sheared.  It  would 
seem  that  after  a  time  the  pre-Cambrian  floor  reached  the  limit 
of  strain  and  broke  into  blocks  which  were  thrust  upward  into 
the  younger  rocks,  but  not  in  all  cases  reaching  the  surface,  as 
now  exposed.  The  folded  younger  rocks  were  caught  at  what- 
ever stage  of  folding  they  had  reached  when  the  gneissic  floor 
broke. 

Later  adjustment  faulting  would  have  probably  caused  some 
slumps  along  the  planes  of  earlier  reverse  faulting. 

Similar  relations  obtain  in  other  portions  of  the  Taconic  belt ; 
as  at  Rutland,  Vermont,  and  in  Dutchess  County,  N.  Y.  at  Stiss- 
ing  Mountain,  near  Stissing  Junction,  at  East  and  Schaghticoke 
mountains  near  Dover  Plains,  at  Corbin  Hill  near  Pawling,  in  the 
Fishkill  Mountains  and  also  at  "Pine  Island"  near  Patterson,  in 
Putnam  County. 

The  great  abyssmal  swell  of  the  pre-Cambrian  floor  caused  it 
to  break  at  numerous  places,  often  pushing  the  gneiss  up  into 
much  younger  strata,  the  gneiss  often  carrying  the  quartzite  with 
it.  Movements  of  lesser  violence  would  have  caused  similar 
breaks  between  younger  rocks  which  would  not  be  so  apparent 
as  where  the  movement  was  violent  enough  to  carry  the  pre- 
Cambrian  against  the  Ordovician  limestone  and  schist. 

THE  PLEISTOCENE. 

Only  incidental  attention  was  given  to  the  surface  deposits. 

Typical  kame  moraine  topography  prevails  over  the  area 
around  Barber  Pond  and  two  miles  north  of  it.  (See  Plate 
LXXIV,  A).  Barber  Pond  is  very  shallow  and  is  surrounded  and 
formed  by  kames.  A  tongue  of  ice  probably  projected  down  the 
valley  from  Bennington  and  the  drainage  from  this  tongue  was 
impounded  in  a  shallow  basin  formed  by  Mann  and  Mason  hills 


370  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

on  the  south  and  the  ice  on  the  north.  In  this  basin  the  kames 
were  built.  They  are  the  marginal  moraine  deposits  of  the  ice  in 
the  valley. 

Northeast  of  Barber  Pond  a  long  serpentine  ridge  rises 
gradually  from  the  flat  ground  just  west  of  Brown's  corner  and 
extends  one-fourth  mile  up  the  hill  in  a  northeasterly  direction 
towards  the  range.  It  has  the  form  of  a  typical  esker  and  was 
probably  formed  when  the  ice  rested  on  the  lower  slope  at  the 
foot  of  the  range.     (See  Plate  LXXIV,  B). 

There  is  evidence  of  border  drainage  along  the  eastern  edge 
of  the  valley  southeast  of  Bennington. 

East  of  Bennington  the  Walloomsac  has  cut  through  a  thick 
bench  of  gravel  and  sand  which  the  stream  built  out  towards  the 
ice  margin  as  it  receded  from  the  range.  This  delta  terrace  ex- 
tends for  two  miles  southward  west  of  Harmon  Hill.  At  the 
time  it  was  forming  the  drainage  of  the  Walloomsac  may  for  a 
time  have  passed  as  a  marginal  stream  along  the  eastern  edge 
of  the  ice  and  around  its  southern  end  to  find  exit  at  the  pass  at 
Pownal  Center. 

On  the  southern  flank  of  Mason  Hill  the  modified  drift, 
which  is  piled  high  above  the  river,  consists  of  thick  deposits  of 
well-sorted  sands  and  gravels  and  probably  represents  deposits 
from  glacial  streams  into  a  lake  at  the  south  during  a  halt  of  the 
ice  in  its  retreat  northwest  along  the  Hoosick  Valley. 

North  of  Bennington  the  typical  knob  and  basin  topography 
is  lacking.  One  or  two  kames  were  noted  on  the  southern  end  of 
West  Mountain. 


STUDIES   IN   THE   GEOLOGY    OF 
WESTERN  VERMONT 


CLARENCE  E.  GORDON,  Ph.  D. 

Professor  of  Geology,  Massachusetts  Agricultural  College 


X^X^'-T.^^ 


From  the  Twelfth  Report,  Vermont  State  Geologist 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  JIS 

tracks  at  Chester  Depot  and  is  equipped  with  Raymond  crush- 
ing machinery,  etc. 

In  spite  of  the  general  car  shortage,  Vermont  talc  companies 
report  no  difficulty  in  moving  their  products. 

The  American  Soapstone  Finish  Company,  Chester  Depot. — 
C.  P.  Dodge,  sole  owner ;  E.  E.  Holt,  superintendent. 

This  company  mines  a  low  grade  talc  from  the  Carleton 
Quarry,  in  Chester,  and  makes  it  into  a  variety  of  substances : 
plaster  board,  soapstone  finish,  dusting  powder  for  tires,  etc.  It 
also  sells  its  product  to  the  roofing  and  paper  trade. 

SOAPSTONE. 

As  already  stated,  the  soapstone  industry  in  Vermont  has 
been  at  a  standstill  for  several  years,  although  this  substance  is 
by  no  means  exhausted. 

Recently  the  Steatite  Electric  Products  Corporation,  of  York- 
town  Heights,  N.  Y.,  has  been  formed  for  the  manufacture  of 
a  new  electric  flatiron,  the  core  of  which  will  be  made  of  soap- 
stone.  It  is  understood  that  this  corporation  has  leased  the  old 
Union  Soapstone  Company's  properties  and  will  supply  itself 
with  soapstone  from  them. 


STUDIES  IN  THE  GEOLOGY  OF  WESTERN  VERMONT. 


Clarence  E.   Gordon, 
Massachusetts  Agricultural  College. 


TABLE  OF  CONTENTS. 

Introduction. 
Physiography. 

The  Green  Mountain  plateau  and  its  ranges. 

The  Vermont  valley. 

The  Taconic  range  and  its  foothills 

The  Champlain  lowland. 
Review  of  the  geological  terranes  of  western  Vermont  and  their  dis- 
tribution. 

Pre-Cambrian. 

Lower  Cambrian. 

Middle  Cambrian. 

Upper  Cambrian. 

Beekmantown  ( Calcif erous ) . 

Chazy. 

Black  River. 

Trenton. 

Utica. 

Later  Ordovician  ("Hudson"). 
General  Structural  Considerations. 

Description  and  discussion  of  field  studies  by  the  writer  in  western 
Vermont. 

Orwell  Township. 

Benson  Township. 

Sudbury  Township. 

Brandon  Township. 

Danby,  Mount  Tabor,  Wallingford,  Tinmouth,  Clarendon,  Rutland, 
Proctor  and  Pittsford. 

Shaftsbury,  Arlington,  Sunderland,  Manchester,  Dorset,  Rupert  and 
Pawlet. 

Pownal,  Stamford,  Bennington,  Woodford,  Shaftsbury  and  Glasten- 
bury. 

Whiting  and  Shoreham. 

Leicester,    Salisbury,   Middlebury,   Cornwall,   Bridport,   Weybridge, 
Addison,  New  Haven,  Waltham  and  Vergennes. 

Burlington. 

St.  Albans  Bay. 

South  Hero  and  Grand  Isle. 
General  summary. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  115 

INTRODUCTION. 

General.  The  writer's  studies  among  the  rocks  of  the 
Taconic  region  were  begun  in  the  summer  of  1906  in  Dutchess 
County,  N.  Y.^  and  were  continued  intermittently  for  several 
seasons,  first  in  the  Hudson  valley  around  Poughkeepsie  and  later 
eastward  into  the  Dover-Pawling  valley  and  the  hills  that  bound 
it  east  and  west.  The  area  at  the  east  proved  so  complex  that 
it  appeared  advisable  to  examine  other  portions  of  the  Taconic 
belt  before  suggesting  any  interpretations  of  the  geological 
structure. 

In  the  summer  of  1912  an  examination  was  begun  of  the 
southwestern  portion  of  the  State  of  Vermont,  in  Bennington 
County.  Although  only  about  three  weeks  were  spent  in  this 
region  a  number  of  interesting  observations  were  made,  and 
because  it  did  not  appear  practicable  to  continue  the  work  with 
the  idea  of  mapping  a  quadrangle,  the  results  obtained  were 
published  in  the  Report  of  the  Vermont  State  Geologist  in  the 
form  of  notes  on  the  geology  in  the  vicinity  of  Bennington.^  The 
work  around  Bennington,  although  hardly  more  than  started, 
opened  up  many  problems  and  served  as  a  stimulus  to  further 
studies  in  western  Vermont  which  it  is  the  object  of  this  paper 
to  describe.  These  later  studies  were  undertaken  with  the  kind 
consent  of  the  State  Geologist. 

The  field  studies  on  which  this  paper  is  based  were  made 
in  part  in  the  summer  of  1918  during  a  three  weeks'  trip  on  foot 
through  the  Vermont  valley  and  portions  of  the  Champlain  low- 
land, from  Bennington  at  the  south  as  far  north  as  Vergennes, 
with  occasional  trips  into  the  mountains  which  hem  in  the  valley 
on  each  side  and  bound  the  Champlain  lowland  on  the  east.  Very 
brief  examination  was  also  made  during  the  same  season  of  the 
formations  around  Burlington  and  along  the  lake  shore  at  Mal- 
letts  and  St.  Albans  bays.  This  trip  was  cut  short  by  an  attack 
of  influenza.  During  parts  of  the  next  two  summers  more  de- 
tailed studies  were  made  in  the  towns  of  Pittsford,  Chittenden, 
Brandon,  Leicester,  Whiting,  Shoreham,  Sudbury,  Orwell,  Ben- 
son and  Hubbardton.  In  addition  the  writer  was  able  in  the 
season  of  1920  to  inspect  with  care  portions  of  the  formations  on 
Grand  Isle,  both  alone  and  in  company  with  the  State  Geologist, 
and  to  review  some  of  the  relations  in  the  vicinity  of  Bennington. 
In  the  season  of  1918  it  was  hoped  to  make  a  more  thorough 
study  of  the  rocks  within  the  slate  belt  and  also  in  the  Green 
Mountain  plateau  than  circumstances  permitted. 

In  all  the  work  it  was  the  practice  to  inspect  as  many  out- 
crops as  possible,  but  especially  in  connection  with  the  studies  in 
Brandon,  Sudbury  and  Orwell,  which  was  a  region  selected  in 

^  Geology  of  the  Poughkeepsie  Quadrangle,  N.  T.   State  Mus.  Bull.   148, 
1911. 

2  Ninth  Report  of  the  State  Geologist,  pp.   337-370. 


116  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

which  to  make  a  wide  surface  section  from  the  Green  Mountains 
to  Lake  Champlain.  The  real  purpose  in  mind  of  getting  a  first- 
hand knowledge  of  some  of  the  important  field  relations  shown 
by  certain  formations  and  their  members  under  various  aspects 
of  deformation  and  erosion  at  widely  separated  places  made  it 
advisable  to  give  a  discursive  but  critical  examination  to  a  rather 
extensive  region. 

Brief  historical  statement.  To  most  people  the  rocks  of 
Vermont  are  known  because  of  the  great  quarries  of  marble  and 
slate  which  have  been  opened  in  them  and  from  the  excellent  de- 
scriptions which  have  been  given  of  these  valuable  assets  of  the 
State.  To  geological  students  the  part  played  by  Vermont  rocks 
in  the  annals  of  American  geology  has  become  known  and  ap- 
preciated through  the  work  of  many  geologists,  among  whom  may 
especially  be  named  that  keen,  patient  and  tireless  investigator, 
Rev.  Augustus  Wing.  Vermont  rocks  also  played  a  part  in  the 
controversy  which  grew  out  of  the  diverse  interpretations  made 
by  different  students  in  efforts  to  unravel  the  difficult  stratigraphy 
and  structure  of  the  Taconic  region.  The  great  controversy  has 
passed  into  history  and  most  of  the  reverberations  of  its  acrimony 
have  died  away;  but  many  differences  of  opinion  have  persisted 
and  probably  always  will.  These  and  the  controversy  itself  have 
served  useful  ends  in  directing  attention  to  a  region  of  much  in- 
terest and  importance  in  the  geology  of  eastern  North  America. 

In  the  end  probably  all  will  have  to  subscribe  to  what  Elkanah 
Billings  wrote  as  long  ago  as  1872,  that,  on  account  of  the  ex- 
tremely complicated  structure  of  the  rocks,  no  man  living  (and 
one  might  add,  or  those  who  are  to  come)  would  ever  see  a  perfect 
map  of  the  Taconic  region.  Nevertheless,  towards  that  end  the 
workers  of  future  generations  will  continue  to  go  forward. 

General  plan  of  the  paper.  The  paper  is  divided  into  two 
somewhat  distinct  and  yet  closely  correlated  parts : 

1.  (a)  The  description  of  the  principal  physiographic  divisions 

of  western  Vermont ; 
(b)  An  account,  accompanied  by  brief  descriptions,  of  the 
characters,    distribution    and    other    features    of    the 
various  formations  with  which  the  paper  deals. 

2.  (a)   The  description  and  discussion  of  a  number  of  observa- 

tions made  by  the  writer  in  various  parts  of  western 
Vermont,  particularly  with  reference  to  the  secondary 
deformations  of  the  different  rocks; 
(b)   Conclusions  reached  or  interpretations  suggested  by  the 
writer. 

A  part  of  the  program  is  avowedly  an  ambitious  one.  It 
should  be  stated  that  any  interpretations  which  are  offered  are 
advanced  with  a  full  appreciation  of  the  difficult  geology  involved 
and  of  the  achievements  and  contributions  of  others  who  have 
labored  to  solve  the  problems  of  the  region. 


PLATE   XXI. 
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PHYSIOGRAPHIC 
Dl  VISIONS 

OF 

WESTERN  VERMONT 

eENERALIZED 

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1ARC1NS   OF    GREEN  TIT.  PLATEAU 

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MASSAC   HUS  ETXS 


118  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

PHYSIOGRAPHY. 

General.  Mention  has  been  made  of  certain  physiographic 
features  of  Vermont  which  for  the  general  reader  require  a  some- 
what further  brief  description.  The  natural  relief  features  and 
to  some  extent  the  political  boundaries  of  a  region  are  landmarks 
which  form  the  framework  on  which  one  hangs,  in  the  form  of 
maps  and  otherwise,  the  description  and  account  of  the  geological 
features.  A  map  is  therefore  offered  to  show  the  principal 
physiographic  divisions  of  western  Vermont.  This  map  may  be 
useful  in  conveying  some  idea  of  the  present  lay  of  the  land.  It 
has,  however,  many  limitations  in  following  any  but  the  most 
recent  geological  processes.  If  the  present  land  forms  and  surface 
conditions  are  too  narrowly  followed  they  may  become  a  source 
of  embarrassment  in  interpreting  the  true  geological  history. 

For  the  purposes  of  the  paper  four  physiographic  divisions 
are  recognized.  The  discussion  of  the  geology  is  inevitably  de- 
veloped about  these  divisions.  As  explained  above,  personal 
observations  have  not  been  made  with  equal  thoroughness  over 
all  four  divisions. 

1.  The  Green  Mountain  Plateau  and  Its  Ranges. 

2.  The  Vermont  Valley. 

3.  The  Taconic  Range  and  Its  Foothills. 

4.  The  Champlain  Lowland. 

GREEN  MOUNTAIN  PLATEAU  AND  ITS  RANGES. 

This  prominent  physiographic  division  from  which  Vermont 
has  derived  its  name,  is  a  broad  upland  which  extends  as  a  wide 
region  lengthwise  across  the  State  from  north  to  south.  It  crosses 
Massachusetts  and  its  counterpart  forms  the  highlands  of  west- 
ern Connecticut,  southeastern  New  York  and  New  Jersey  and 
may  be  traced  to  Pennsylvania  and  beyond.  Northward  it  passes 
into  the  Province  of  Quebec.  The  western  portion  of  this  divi- 
sion which  extends  from  New  Jersey  northward  into  Canada 
was  designated  by  Dana^  as  the  "protaxis"  of  the  Appalachian 
chain,  which  extends  from  Alabama  to  Canada. 

In  their  present  development  the  Green  Mountains  form  an 
elevated  plateau  throughout  their  extent.  In  Vermont  the  plateau 
is  already  deeply  trenched  by  some  rivers,  particularly  in  its  north- 
ern part,  and  more  or  less  incised  by  tributary  and  other  streams. 
On  the  whole  its  rugged  outlines  give  it  a  youthful  aspect,  which 
may  be  attributed  in  part  to  the  resistant  character  of  its  rocks. 

Generally  speaking,  the  surface  is  broadly  undulating  and 
averages  roughly  about  2,000  feet  above  sea-level.  There  are 
numerous  rather  broad  areas  about  500  feet  higher,  and  numerous 
peaks  and  ridges  rising  to  and  above  3,000  feet.  Mt.  Mansfield, 
the  highest  elevation,  is  4,406  feet  high.     The  sharper  elevations 

1  Manual,  Fourth  Edition,  p.  24. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  119 

which  may  be  thought  of  as  the  more  distinctly  ridge-hke  elements 
of  the  plateau,  in  the  northern  part  of  the  State  form  two  rather 
distinct  ranges  which  merge  into  one  in  the  southern  half. 

The  highest  peaks  of  the  State  are  all  only  a  few  miles  distant 
from  the  western  edge  and  succeed  one  another  along  a  line  that 
suggests  a  prominent  general  structural  axis  which  rather  closely 
parallels  the  western  margin  of  the  plateau.  This  margin  is 
marked  for  long  reaches  by  a  prominent  scarp  or  by  a  series  of 
cliffs.  It  begins  in  Pownal  in  Bennington  County  and  follows 
a  north-northeast  direction  to  the  northeastern  part  of  Manchester 
township  and  thence  has  a  general  northerly  direction  to  about 
the  latitude  of  Pittsford.  Then  it  bends  slightly  to  west  of 
north  and  is  sharply  distinct  as  far  north  as  Monkton.  North 
of  Monkton  it  appears  more  broken  in  character,  but  a  general 
return  to  a  north  by  east  course  can  be  discerned.  The  margin 
as  thus  described  has  embayments  at  places  from  Pownal  north- 
ward. The  structural  and  physiographic  axes  often  have  sug- 
gestive coincidence,  afthough  there  are  variations  whose  import 
is  not  clear. 

While  generally  well  settled  and  intersected  by  roads,  some 
of  which  cross  the  plateau  into  the  valley  at  the  west,  there  is  a 
wide  strip  along  the  western  portion,  from  the  Massachusetts 
boundary  northward  two-thirds  the  way  across  the  State,  which 
has  only  a  few  roads  and  is  still  mostly  a  wilderness. 

THE   VEEMONT   VALLEY. 

Directly  west  of  the  Green  Mountain  plateau,  and  extend- 
ing from  Pownal  to  Brandon,  lies  the  "Valley  of  Vermont."  The 
topographic  break  between  the  two  divisions  is  generally  abrupt. 
The  western  margin  of  the  plateau  upland  is  usually  bold,  often 
precipitous.  The  streams  which  come  down  from  it  to  the  valley 
have  not  strongly  impressed  their  drainage  upon  the  plateau. 

In  its  present  topographic  stage  of  development  this  division 
is  only  a  relative  lowland  between  the  Green  Mountains  on  the 
east  and  the  rugged  Taconic  range  on  the  west.  In  its  southern 
part  the  lowest  contours  are  540  feet  along  the  Walloomsac 
River  near  Bennington,  and  620  feet  along  the  Batten  Kill  at 
Arlington.  Along  the  course  of  Otter  Creek  from  Danby  north- 
ward the  contours  descend  from  660  feet  to  340  feet  near  Bran- 
don, where  the  Vermont  valley  merges  with  the  Champlain 
lowland. 

The  floor  of  the  valley  is  in  fact  almost  throughout  a  moderate 
upland  which  is  obscured  by  the  higher  lands  which  hem  it  in.  It 
is  mostly  uneven  and  studded  with  hills.  The  average  relief  is 
probably  above  800  feet.  The  valley  form  is  not,  as  one  unac- 
quainted with  it  might  infer,  such  as  would  have  been  produced  by 
a  single  master  river  running  through  it. 


120  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

North  and  south  of  Bennington,  around  the  head  streams  of 
the  Walloomsac  River,  this  division  is  about  six  miles  wide.  To 
the  west  along  the  river  it  passes  by  a  broad  gap  into  the  Hudson 
valley  lowland.  At  Bennington  the  Vermont  valley  is  offset  two 
miles  to  the  east  and  in  Pownal  is  completely  intercepted  by  the 
Mount  Anthony-Mason  Hill  ridge.  Towards  the  north  in  Sun- 
derland it  narrows  to  a  width  of  two  miles.  It  widens  again  near 
Manchester  around  the  head  streams  of  the  Batten  Kill  and  the 
Mettawee.  North  of  Manchester  it  is  interrupted  by  Dorset 
Mountain  and  here  is  about  one-fourth  of  a  mile  wide.  North  of 
Dorset  Mountain  the  major  valley  is  broken  into  minor  ones  by 
prominent  intermediate  ridges.  Otter  Creek  occupies  the  eastern 
minor  valley,  which  from  WalHngford  to  Rutland  is  over  three 
miles  wide.  As  the  topographic  map  shows  the  creek  changes 
direction  at  Rutland  from  north  to  west,  crossing  the  structural 
axes  of  the  rock  formations ;  but  at  Center  Rutland  the  stream 
regains  a  general  northerly  direction  and  flows  through  a  narrow 
valley  to  Proctor.  Thence  it  passes  into  the  open  valley  of  Pitts- 
ford  which  leads  into  Brandon.  In  Brandon  the  major  valley 
has  a  more  uniform  surface  and  widens  out  northward  to  form 
the  Champlain  lowland. 

The  Vermont  valley  has  its  physiographic,  and  to  a  consider- 
able extent  also  its  geological,  counterpart  in  the  Berkshire  valley 
of  western  Massachusetts  along  the  upper  reaches  of  the  Hoosic 
and  Housatonic  rivers.  There  is  a  recognizable  apparent  simi- 
larity in  general  configuration  between  the  two,  and  in  the  modifi- 
cations occasioned  by  hills,  ridges  and  outlying  masses  of  the  other 
physiographic  divisions. 

The  Berkshire  valley  continues  into  Connecticut,  but  at 
Canaan  the  Housatonic  leaves  a  wide  valley  for  a  narrow  one 
across  the  upland,  which  in  Connecticut,  however,  has  a  lower 
average  elevation  than  in  Massachusetts  and  Vermont.  In  north- 
western Connecticut  and  southeastern  New  York  irregularities 
appear  consequent  upon  the  geological  structure  and  relations 
there  present. 

THE  TACONIC  EANGE  AlfD  ITS  FOOTHILLS. 

The  Taconic  range  bounds  the  Vermont  valley  on  the  west 
throughout  its  length,  except  for  erosion  gaps,  the  widest  of 
which  is  west  of  Bennington.  In  Vermont  this  division  is  the 
continuation  of  a  similar  range  that  lies  along  the  border  between 
Massachusetts  and  New  York.  It  extends  in  Vermont  from 
Shaftsbury  in  the  southwestern  part  of  the  State  to  Orwell  and 
Sudbury.  North  of  Pownal  practically  all  the  range  is  in  Ver- 
mont and  all  the  higher  summits  are  in  this  State.  Viewed  as  a 
broad  unit  the  range  overlaps  the  New  York- Vermont  boundary 
in  its  southern  half.     North  of  Rupert  the  western  margin  hugs 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  121 

the  State  line  as  far  as  Poultney,  whence  it  passes  due  north  to 
Orwell  and  Sudbury. 

In  its  course  across  Vermont  the  relation  of  the  range  to  the 
Vermont  valley  is  marked  by  at  least  two  prominent  structural 
irregularities.  Southwest  of  Bennington,  in  correspondence  with 
offset  in  the  Vermont  valley  already  mentioned,  Mt.  Anthony 
lies  farther -east  than  does  West  Mountain  in  Shaftsbury,  and  in 
the  town  of  Dorset  the  mass -of  Dorset  Mountain  rises  abruptly  in 
the  valley  midway  in  its  course  from  Bennington  to  Brandon. 

The  higher  elevations  of  this  division  range  from  about  2,500 
feet  to  about  3,500  feet  above  sea-level.  Equinox  Mountain 
reaches  3,816  feet  and  Dorset  Peak  is  3,804  feet  high.  Most  of 
the  higher  summits  lie  along  the  eastern  border  of  the  range. 
West  and  north  the  surface  falls  off  in  elevation  into  the  foothill 
region ;  but  many  scarps  and  precipices  marking  probable  fault 
lines  greatly  disturb  the  surface  regularity  and  contribute  notably 
to  the  present  topographic  outlines.  Although  symmetry  of  con- 
tours is  therefore  lacking  in  the  present  stages  of  topographic 
development  if  one  were  to  generahze  very  broadly  the  northern 
and  western  slopes  of  the  division,  the  erosion  features  of  the 
elevation  would  fall  off  gradually  westward  and  northward  by 
slopes  of  similar  gradient  to  the  relative  lowlands  of  the  Hudson 
and  Champlain  valleys. 

This  division  is  cut  across  and  otherwise  by  streams  whose 
branches  heading  rather  deeply  into  it  have  dissected  it  into  a 
series  of  peaks  and  ridges.  In  its  outlines  the  division  offers 
some  contrasts  with  western  edge  of  the  Green  Mountain  plateau ; 
but  stream  incision  has  not  been  pronounced  in  either  wall  of 
the  valley  and  the  topographic  outlines  of  its  two  slopes  wear 
much  the  same  expression  for  long  distances. 

The  valleys  which  cut  through  the  range  mark  the  extension 
of  the  lower  Hudson  valley  levels  into  the  intermediate  upland  of 
the  Vermont  valley.  There  are  certain  notable  differences  among 
these  valleys  which  may  be  mentioned  here.  The  valley  of  the 
Walloomsac  River  is  wide  and  is  really  a  broad  extension  of  the 
Vermont  valley  westward.  That  of  the  Batten  Kill  is  narrower 
and  hemmed  in  by  steeper  slopes.  The  valley  formed  by  the 
Mettawee  and  the  West  Branch  of  the  Batten  Kill  is  fairly  wide 
and  the  bottom  lands  are  well  developed.  The  valley  of  Castle- 
ton  River  is  rather  narrow  and  its  northern  are  steeper  than  its 
southern  slopes,  as  nearly  all  its  branches  within  the  range  come 
in  from  the  south. 

THE   CHAMPLAIN  LOWLAND. 

The  distinctness  of  this  physiographic  division  as  a  whole  is 
sharper  when  viewed  from  a  distance  in  broad  sweeps  rather 
than  from  a  close  examination  of  the  topography  of  its  surface, 
which,  like  that  of  the  Vermont  valley  is  studded,  in  some  places 


122  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  ^ 

more  than  in  others,  with  hills.  It  may  first  be  described  in  its 
larger  outlines. 

Lake  Champlain  lies  along  its  western  border,  and  rising  from 
the  western  side  of  the  lake,  with  their  bases  dipping  into  it  at 
places  or  separated  from  the  lake  shore  by  a  narrow  strip  of 
hilly  land,  stand  the  rugged  Adirondacks.  In  its  southwestern 
portion  it  is  bounded  by  the  northwestern  foothills  of  the  Taconic 
range.  The  boundary  at  the  southwest  swings  eastward  around 
the  Orwell  hills  and  then  encloses  a  narrow  embayment  extend- 
ing up  the  valley  of  the  Lemon  Fair  River  between  the  Orwell 
and  Sudbury  hills.  It  then  passes  around  the  northern  end  of 
the  Sudbury  hills  to  Brandon  and  thence  northerly  along  the  west- 
ern base  of  the  Green  Mountain  plateau,  with  the  topographic 
break  sharply  outlined  between  the  lowland  and  tlje  plateau  as 
far  north  as  Monkton.  North  of  Monkton  the  Green  Mountain 
plateau  surface  is  more  broken  along  the  edge;  but  the  higher 
average  relief  is  well  enough  preserved  to  give  an  outline  to  the 
Champlain  valley  in  its  extension  northeastward  to  the  Canada 
line.  At  the  north  the  Champlain  lowland  merges  with  the  St. 
Lawrence  valley.  At  the  south  along  the  narrow  region  of  the 
lake  it  joins  with  the  Hudson  valley. 

The  lowest  surface  in  this  division  is  that  of  Lake  Champlain, 
which  for  high  and  low  water  conditions  averages  about  100  feet 
above  sea-level.  But  the  lake  occupies  a  depression,  the  actual 
depth  of  whose  rock  bottom  will  probably  never  be  known,  as  it 
could  hardly  have  escaped  being  modified  by  glacial  deposits. 
Soundings  have  shown  that  the  waters  now  fill  a  basin  of  vary- 
ing depth  and  bring  out  in  the  channel-Hke  character  of  its  west- 
ern portion  the  indication  of  former  stream  erosion.  The  max- 
imum depth  reached  is  about  400  feet  near  Essex,  N.  Y.,  but  the 
present  bottom  ranges  from  that  depth  to  comparatively  shallow 
water.  The  bottom  of  the  lake  in  many  places  thus  stands  in 
marked  contrast  with  even  the  lowest  portion  of  the  present  ex- 
posed surface  of  this  lowland.  The  lake  has  many  low  islands 
of  varying  dimensions  throughout  its  extent. 

Between  Lake  Champlain  on  the  west  and  the  Green  Moun- 
tains on  the  east  for  a  distance  of  about  40  miles  from  the 
northern  end  of  the  Taconic  range  to  BurHngton,  converging 
somewhat  towards  BurHngton,  and  again  north  of  Georgia  through 
St.  Albans  and  Highgate  to  the  Canada  line,  a  large  portion  of 
the  surface  ranges  from  about  100  feet  at  the  lake  to  350  feet 
inland,  with  the  rest  of  it  from  350  to  over  400  feet.  Along  parts 
of  the  Otter  Creek  valley  and  along  the  lake  for  a  width  of  about 
six  miles,  in  the  areas  just  described,  the  contours  are  relatively 


PLATE   XXIII. 


t 


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o^'^^^i;: 


^1  B^^^S'i-- 

/;   A>y^"V/  -i^S'  nPA  ^rr-  ^4,._ 


Township  Map   of  Vermont. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  123 

widely  spaced  and  run  long  distances  without  closing.  There  is 
distinguishable  a  low  range  of  hills  extending  north  from  Orwell, 
which  is  so  reduced  over  most  of  its  surface  as  hardly  to  deserve 
the  name,  but  which  is  noticeable  by  reason  of  the  lower  land 
along  the  lake  and  from  the  excavation  of  Otter  Creek  on  the 
east.  This  range  reaches  its  greatest  altitude  in  Snake  Mountain 
(1,271  feet)  and  terminates  in  Buck  Mountain  (927  feet)  south 
of  Vergennes.  Mt.  Philo  in  Charlotte  is  968  feet  high.  In 
Bristol  and  Monkton  there  are  prominent  hills  including  Hogback 
(1,220  feet),  and  several  conspicuous  hills  occur  west  and  north 
of  Lake  Dunmore.  St.  Albans  Hill  (910  feet)  and  Aldis  Hill 
(840  feet)  are  the  conspicuous  elevations  north  of  Georgia.  The 
Orwell-Buck  Mountain  ridge  at  the  south  merges  topographic- 
ally with  the  western  foothills  of  the  Taconic  range. 

In  late  Pleistocene  time  much  of  the  Champlain  lowland  was 
covered  probably  by  the  waters  of  the  sea  which  probably  ex- 
tended into  the  Vermont  valley  as  far  south  as  Rutland.  The 
present  surface,  both  on  the  islands  of  the  lake  and  on  the  main- 
land, gives  clear  evidence  of  the  former  submergence  of  a  wide 
portion  of  this  lowland  by  an  inland  water  body. 

North  of  the  Winooski  River  to  the  latitude  of  Georgia  the 
surface  has  a  more  uniform  and  a  uniformly  higher  elevation, 
ranging  from  300  to  350  feet.  The  contours  are  more  narrowly 
spaced  and  close  within  short  distances,  giving  a  more  cut-up 
topography. 

Four  streams,  Otter  Creek,  and  the  Winooski,  Lamoille  and 
Missisquoi  rivers,  cross  the  lowland  to  enter  Lake  Champlain. 

REVIEW    OF    THE    GEOLOGICAL    TERRANES     AND 

FORMATIONS  OF  WESTERN  VERMONT  AND 

THEIR  DISTRIBUTION. 

General  remarks.  A  short  acquaintance  with  the  rocks  of 
western  Vermont  in  their  field  relations  will  soon  convince  one 
that  they  have  had  a  long  and  varied  history,  that  their  present 
geography  is  very  different  from  that  which  existed  at  various 
times  in  the  past,  and  that  many  of  them  are  now  remote  from 
the  positions  which  they  once  occupied. 

The  general  geology  of  areas  contiguous  to  Vermont  and 
extending  for  some  distance  north  and  south  of  the  State  shows 
that  while  the  Vermont  rocks  have  had  in  some  ways  an  inde- 
pendent history  they  are  in  a  broad  way  genetically  related  in 
age  and  perhaps  quite  as  much  so  in  certain  general  structural 
characters  to  rock  formations  over  an  extensive  region. 

It  is  more  or  less  widely  recognized  that  many  similarities 
in  the  age  and  structural  relations  of  the  rocks  over  this  wide 
region  permit  a  certain  amount  of  generalization  with  regard  to 
broad  crustal  movements  concerned  in  their  deposition.  Account 
has  been  taken  of  great  tectonic  displacements  which  are  known 


124  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

to  have  occured,  in  explaining  the  absence  of  certain  strata,  or 
better  perhaps  certain  faunas,  over  the  entire  region  and  the  ap- 
parent limitations  of  others ;  but  these  phenomena  have  also  been 
explained,  at  least  in  part,  on  the  basis  of  minor  crustal  move- 
ments which  have  operated  to  cut  off  faunal  provinces  from  each 
other  and  to  restrict  the  areas  of  continental  seas. 

As  investigations  have  extended  our  information  concerning 
details  of  stratigraphy  we  have  had  positive  confirmation  of  the 
wide  extension  of  certain  ancient  seas  within  the  region.  On  the 
other  hand  extensive  study  has  failed  to  reveal  any  conclusive 
evidence  of  the  former  presence  of  certain  seas,  which  are  gen- 
erally assumed  to  have  been  wholly  absent,  or  the  wider  exten- 
sion of  others,  whose  faunas  are  present  in  places,  and  whose 
ancient  boundaries  are  set  on  the  basis  of  known  outcrops. 

From  the  nature  of  the  complex  geological  relations  now 
present  the  explanations  of  these  absent  intervals  cannot  be  based 
upon  positively  identified  depositional  unconformities  between 
younger  and  older  rocks  than  those  which  are  absent.  It  is,  of 
course,  necessary  to  recognize  the  possible  existence  of  erosion 
intervals  of  varying  degrees  of  duration  among  sedimentary 
formations,  due  to  periods  of  restlessness  of  the  internal  forces 
which  disturb  the  crust,  but  one  must  also  consider  the  evidence 
that  the  crust  may  apparently  remain  relatively  quiet  for  immense 
intervals  of  time,  and  particularly,  for  the  region  of  western 
Vermont  and  related  areas,  it  is  necessary  to  take  account  of  the 
evidence  of  profound  crustal  displacements  and  metamorphism, 
and  of  erosion  at  various  periods  of  the  region's  history. 

It  has  not  been  clear  just  how  far  it  would  be  well  to  go  for 
the  profit  of  the  general  reader  as  well  as  for  the  more  precise 
information  of  the  geological  student  in  reviewing  the  characters, 
variations  and  distribution  of  the  different  terranes  and  forma- 
tions of  the  region  under  discussion.  It  is  clear  that  some  idea  of 
these  different  rocks  and  the  confusion  that  prevails  among  them 
in  the  field  should  be  given  as  an  aid  to  the  discussion  that  will 
follow. 

A  categorical  statement  of  such  matters  is  likely  to  leave  an 
impression  of  simplicity;  but  care  will  be  taken  in  the  sequel  to 
point  out  the  many  difficulties  that  lie  in  the  way  of  positive  de- 
terminations of  field  relations  and  that  conclusions  are  based  on 
what  seems  most  probable,  with  the  evidence  at  hand,  among 
several  possibilities  that  are  presented. 

The  following  descriptions  are  purposely  given  with  con- 
siderable fullness,  but  structural  considerations  are  largely  post- 
poned for  later  treatment. 

PRE-CAMBRIAN. 

According  to  many  observers  the  pre-Cambrian  basement,  or 
old  sea  floor,  on  which  the  Lower  Cambrian  rocks  of  this  general 
region  were  deposited,  is  decisively  exposed  at  various  places 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  125 

in  the  Green  Mountain  plateau.  The  rocks  which  have  been 
described  as  pre-Cambrian  consist  of  gneisses,  which  are  notably 
chiefly  of  probably  igneous  origin,  and  otiier  rocks  such  as  schists, 
quartzites,  graywackes  and  crystalline  limestones. 

The  discrimination  of  the  pre-Cambrian  is  most  satisfactory 
in  those  places  at  which  a  heavy  basal  quartzite,  or  a  conglomerate, 
appears  to  rest  unconformably  upon,  or  to  be  separated  by  a 
thin,  schistose  layer  from  a  rock  whose  structural  features  are 
in  pronounced  discordance  with  those  of  the  younger  rock,  and 
are  apparently  of  much  more  ancient  date.  In  Massachusetts  and 
New  York  similar  relations  have  been  described  and  seem  to 
leave  no  doubt  of  the  exposure  at  the  present  surface  of  a  pre- 
Cambrian  core  in  the  Green  Mountains.  That  certain  old  gneisses 
antedated  the  Cambrian  and  formed  its  floor  of  deposition  is  sub- 
stantially borne  out  by  numerous  localities  where  the  advancing 
Cambrian  sea  caught  and  preserved  portions  of  the  regolith  of 
the  land  which  it  was  overlapping.  The  more  or  less  decayed 
material  seems  to  have  been  only  partially  sorted  at  times  and 
seems  to  have  taken  on  in  greater  or  less  degree  the  bedded 
structure  of  the  Cambrian  while  grading  at  depth  into  less  altered 
rock  which  retained  more  or  less  of  the  structure  of  the  parent 
gneiss.  Such  relations  seem  especially  significant  with  respect 
to  the  question  of  depositional  unconformity  in  a  region  that 
gives  evidence  of  more  than  one  orogenic  movement  and  of  pro- 
found overthrusting ;  for  it  is  conceivable  that  contacts  of  pure 
quartzite,  or  even  conglomerate,  could  in  such  a  region  be  the 
results  of  other  processes  than  marine  overlap.  It  will  be  noted 
later  also  that  there  are  numerous  places  in  western  Vermont 
where  Ordovician  limestones  apparently  rest  by  unconformity  on 
rock  that  appears  to  be  Cambrian  without  any  traces  of  a  basal 
transgressive  sand  or  other  rock  intervening. 

The  separation  of  the  Vermont  pre-Cambrian  into  systems 
such  as  have  been  recognized  elsewhere  is  a  task  which  has  yet 
to  be  worked  out  for  the  Green  Mountain  plateau  generally.  In 
various  parts  of  the  plateau  Whittle,  Keith  and  others  have  de- 
scribed as  probably  pre-Cambrian  various  metamorphic  rocks 
such  as  quartzite,  schists  and  crystalline  limestones  which  have 
been  called  Algonkian,  Huronian  and  so  forth.  Similar  rocks 
have  been  described  for  Massachusetts,  New  York  and  Quebec. 
The  discrimination  of  older  rocks  from  altered  Paleozoic  has  not 
always  been  made  with  a  sharpness  that  is  conclusive. 

While  there  is,  generally  speaking,  an  abrupt  passage  from 
the  less  metamorphosed  rocks  of  western  Vermont  to  those  of 
the  plateau  this  fact  by  itself  is  discounted  somewhat  by  the  un- 
doubted upthrust  or  overthrust  relation  of  the  plateau  to  the  rocks 
at  the  west  of  it.  It  is  somewhat  significant,  although  exhaustive 
search  has  yet  to  be  made,  that  in  northwestern  Vermont  no  pre- 


126  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Cambrian  basement  contacts  have  yet  been  discovered  to  the 
Paleozoic  rocks. 

In  spite  of  metamorphism  and  apparent  absence  of  fossils, 
investigations  have  already  extended  the  range  of  Paleozoic  seas 
over  this  region,  although  it  remains  to  show  that  in  some  cases 
these  were  the  same  seas  that  laid  down  the  rocks  of  what  is  now 
western  Vermont. 

In  western  Massachusetts  Professor  Emerson  early  suggested 
a  separation  of  the  pre-Cambrian,  and  in  early  descriptions  of 
certain  rocks  he  used  the  term  Algonkian.  Coming  in  later  years 
apparently  to  a  more  conservative  view  he  called  the  pre-Cambrian 
rocks  of  western  Massachusetts,  Archaean,  and  the  Green  Moun- 
tain plateau  a  "broad  Archaean-Silurian  upland." 

The  basal  Cambrian  quartzite  has  been  found  some  distance 
eastward  from  the  western  outcrops  of  the  gneisses  in  Vermont, 
Massachusetts  and  elsewhere  where  it  has  been  preserved  by 
down-folding  or  down-faulting  as  erosion  outliers.  The  quartzite 
or  its  probable  equivalent  extends  for  miles  as  a  fringe  along  the 
western  margin  of  the  plateau.  Throughout  the  ages-long  history 
of  these  rocks  we  may  beHeve  it  has  in  some  way  been  protected 
from  erosion.  It  is  plausible  that  conditions  were  not  favorable 
for  the  preservation  of  vast  areas  of  Cambrian  beds,  and  possibly 
also  later  ones,  elsewhere  in  what  is  now  the  plateau. 

West  of  the  Green  Mountains  presumably  the  pre-Cambrian 
extends  at  unknown  depth  beneath  the  rocks  now  present  at  the 
surface. 

CAMBRIAN. 
Lower  Cambrian. 

The  Lower  Cambrian  has  been  described  as  represented  in 
Vermont  by  the  following-named  formations : 

1.  "Vermont  Formation." 

2.  Dolomite  and  a  quartzite-dolomite  interbedded  series. 

3.  "Red  Sandrock." 

4.  "Georgia  Slates"  ("Georgia  Group"). 

5.  "Roofing  Slates"  (with  associated  rocks). 

Parts  of  all  these  formations  were  presumably  contempora- 
neous and  lithological  differences  were  presumably  due  to  different 
conditions  of  deposition.  Certain  members  of  the  Vermont 
Formation  can  be  reasonably  shown  to  be  basal  and  conformable 
to  the  dolomite.  The  interbedded  series  in  some  places  lies  on 
the  dolomite  and  this  seems  to  be  the  normal  succession.  There 
has  been  so  much  disturbance  of  the  region  that  the  present  rela- 
tions are  sometimes  obscure.  In  some  places  the  interbedded 
series  apparently  lies  on  quartzite  of  the  Vermont  Formation. 
The  Red  Sandrock  has  been  described  as  conformably  subjacent 
to  the  Georgia  Slates  in  northwestern  Vermont.  As  indicated 
above  the  base  of  the  Vermont  Formation  and  its  pre-Cambrian 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  127 

contact  has  been  fairly  conclusively  demonstrated ;  but  the  deposi- 
tional  bases  of  the  Red  Sandrock  and  the  Roofing  Slates  are 
unknown. 

Each  formation  presents  horizontal  differences  which  are 
better  shown  in  some  than  in  others.  In  all  cases  the  intrarela- 
tionships  and  the  relations  of  the  formations  to  each  other  and 
to  associated  rocks  are  much  confused  and  disguised  by  deforma- 
tions which  the  rocks  have  suffered. 

The  Vermont  Formation.  The  Vermont  Formation  has  the 
following-named  members  at  various  places  throughout  its  extent 
at  the  present  surface : 

a.  Various  basal  gneisses  or  schists,  probably  altered  deriva- 
tives in  most  cases  of  pre-Cambrian  gneisses  and  other  rocks, 
sometimes  rather  sharply  delaminated  from  the  parent  rock,  but 
often  imperfectly  transitional  between  gneiss  and  quartzite,  con- 
glomerate, or  arkose. 

b.  Arkoses. 

c.  Conglomerate. 

d.  Granular  quartz  rock. 

e.  Massive  brownish  quartzites. 

f.  Schistose  quartzites  and  schists. 

The  first-named  have  been  described  by  different  observers. 
Conglomerate  is  not  uncommon,  sometimes  arkosic.  White, 
granular  quartzites  are  very  common  and  pass  into  massive, 
brownish  rocks,  which  in  turn  grade  into  schistose  quartzites. 
The  massive  quartzites  with  conspicuous,  white,  granular  mem- 
bers are  of  great  apparent  thickness  and  prominence  in  scarps 
along  the  western  front  of  the  Green  Mountain  plateau  and  by 
faulting  are  also  widely  distributed  along  the  Vermont  valley. 

By  thrusting,  members  of  this  formation  may  have  been  car- 
ried westward  into  the  Taconic  division,  but  this  question  will 
be  discussed  beyond. 

Fossils  in  the  quartzite  (and  the  limestones)  together  with 
the  field  relations  fix  the  age  of  these  various  rocks  certainly  in 
some  cases  and  probably  in  the  others,  as  Lower  Cambrian, 

Dolomite  and  the  interhedded  series.  This  formation  con- 
tains : 

a.  At  some  places  at  least,  at  the  base,  a  limestone  of  mod- 
erate thickness ;  at  other  places  at  the  base  a  dolomitic  limestone 
of  uncertain  thickness. 

b.  Above  (a)  a  succession  of  dolomitic  limestones  inter- 
bedded  with  calcareous  quartzites,  rather  pure,  massive  quartzites 
and  schistose  quartzites. 

In  the  interhedded  series  the  quartzitic  members  seem  to  be 
more  abundant  near  the  base.  The  more  purely  siliceous  mem- 
bers range  in  thickness  from  about  2  inches  to  one  bed  at  least 
10  feet  thick,  possibly  20  feet,  unless  folded.  The  dolomitic 
members  range  from  a  few  inches  to  about  3  feet  in  thickness. 


128  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

The  interbedded  series  is  extensively  developed  along  the 
Vermont  valley  from  Bennington  northward  and  was  traced  by 
the  writer  as  far  north  as  East  Middlebury.  It  is  best  shown 
among  the  hills  along  the  eastern  portion  of  the  valley  and  forms 
the  visible  part  of  most  of  the  camel-hump  arches  that  make  up 
the  valley  floor.  The  outcrops  of  the  members  of  this  series  are 
conspicuous  features  and  the  quartzites  have  undoubtedly  been 
important  factors  in  preservation  from  erosion.  The  series  is 
often  clearly  present,  beneath  the  surface  in  places  intermediate 
between  the  hills  just  mentioned.  The  westward  extension  of 
these  rocks  and  their  relations  to  other  terranes  will  be  discussed 
at  other  places. 

The  intimate  association  of  this  series  with  quartzite  of  the 
Vermont  Formation  is  clear  at  many  places  along  the  Vermont 
valley.  At  Bennington  the  succession  from  quartzite  of  the 
Vermont  Formation  through  dolomitic  limestone  to  interbedded 
limestones  and  quartzites  is  particularly  clear  (see  fig.  21).  The 
two  formations  have  plainly  been  deformed  together  in  a  large 
way,  although  the  interbedded  rocks  appear  to  have  suffered  some 
independent  deformation  both  with  regard  to  folding  and  faulting. 

The  present  distribution  of  the  series  tells  nothing  about  its 
original  horizontal  extent. 

Red  Sandrock.  This  name  has  been  and  is  now  applied  to 
a  formation  that  shows  much  variation  in  composition  and  in 
color,  and  which  in  some  localities  is  chiefly  dolomite.  The  forma- 
tion is  practically  restricted  in  its  outcrops  to  the  west  central 
and  northwestern  parts  of  the  State.  It  is  prominent  at  the 
present  surface  around  Monkton,  at  Snake  Mountain  in  Wey- 
bridge  and  Addison,  at  Buck  Mountain  in  Waltham,  and  thence 
northward  through  Charlotte,  Shelburne,  Burlington  and  beyond. 
At  the  south  in  Addison  County,  and  also  along  the  shore  of  Lake 
Champlain  in  Shelburne  and  BurHngton,  much  of  this  rock  is  a 
quartzite  and  often  has  a  dark,  brick-red  color.  In  Chittenden 
and  Franklin  counties  it  is  described  as  prevailingly  dolomitic. 
In  Georgia,  as  early  described  by  Walcott,  it  consists  of  a  series 
of  bluish  gray,  steel  gray,  gray  massive,  and  reddish  pink  dolo- 
mitic limestones  and  gray,  massive,  arenaceous  limestone,  variously 
banded,  colored,  or  mottled,  and  passes  upward  into  the  Georgia 
Slates. 

At  the  Canadian  line,  according  to  Logan,  it  consists  of  white 
and  red  dolomites  and  sandy  layers,  with  some  strata  mottled  red 
and  white  and  a  few  brick-red.  Some  beds  were  said  to  be  very 
siliceous.  All  weather  yellowish  or  reddish  brown.  The  Red 
Sandrock  series  extends  across  the  Canada  line  for  about  five 
miles. 

The  quartzitic  members  are  all  more  or  less  calcareous  and 
the  dolomitic  beds  are  all  somewhat  siliceous. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  ^29 

The  base  of  this  formation  is  not  known.  The  formation 
has  been  described  by  some  observers  as  merging  with  the  quartz- 
ite  of  the  Vermont  Formation  near  Monkton. 

Lower  Cambrian  fossils  have  been  found  at  various  places 
and  within  different  phases  of  this  formation. 

Along  the  lake  shore  at  and  near  Burlington,  members  of 
this  formation  can  be  seen  to  rest  by  thrust  on  younger  (Ordovi- 
cian)  rocks. 

Except  for  certain  marked  features  of  color  the  Red  Sand- 
rock  series  bears  much  resemblance  in  general  sequence  to  the 
quartzite  and  its  overlying  dolomite  and  interbedded  series  that 
have  been  described. 

Georgia  Slates  {"Georgia  Group/'  "Georgia  Slate  Group''). 
The  members  of  this  group  were  first  described  from  the  town 
of  Georgia  by  C.  D.  Walcott  and  were  represented  as  conform- 
ably succeeding  the  Red  Sandrock  series.  The  group  is  typically 
developed  in  the  towns  of  Georgia,  St.  Albans,  Swanton  and  High- 
gate  in  Franklin  County. 

Walcott  distinguished  a  series  somewhat  as  follows,  begin- 
ning at  the  base : 

a.  Argillacio-micaceous  and  arenaceous  shales,  with  many 
Lower  Cambrian  fossils  ("Georgia  Shales"),  200  feet. 

b.  Argillaceous  shales  with  occasional  layers  of  hard  gray 
limestone,  ^4  inch  to  2  inches  thick,  3,500  feet. 

c.  Light  gray  quartzite,  50  feet. 

d.  Gray  limestone  in  massive  layers,  with  intercalated  bands 
of  argillaceous  shale,  1,700  feet. 

e.  Argillaceous  shales  similar  to  (a)  conformable  at  base 
with  (d)  and  cut  oflf  at  the  top  by  a  fault,  3,500-4,500  feet. 

The  total  thus  gave  the  extraordinary  maximum  thickness 
of  9,950  feet.  The  correlation  was  mostly  with  Lower  Cambrian. 
In  1891  Walcott  described  (d)  of  the  above  as  appearing  to  be 
a  great  lenticle  of  limestone  and  the  fossils  as  approaching  the 
Upper  Cambrian  (in  the  absence  of  Olenellus). 

Ulrich  has  "hazarded"  the  opinion  that  the  upper  3,500  feet 
of  the  shale  of  the  section  described  by  Walcott  may  be  of  "Cana- 
dian" age  (basal  Ordovician).  He  also  questions  the  age,  in  the 
stratum  of  limestone  and  shale  to  which  Walcott  assigned  a 
thickness  of  1,700  feet,  of  a  limestone  which  gives  fossils  that 
may  be  of  Middle  Cambrian  age. 

The  thickness  assigned  the  series  and  other  features  may 
have  to  be  revised  by  future  study  of  the  deformations  of  the 
region. 

Roofing  Slates  (and  associated  rocks).  From  the  northern 
end  of  the  Taconic  region  southward  along  its  western  slopes, 
forming  in  Vermont  a  strip  8  to  11  miles  wide  north  of  Fairhaven 
and  a  strip  from  2  to  3  miles  wide  south  of  Fairhaven  to  West 
Rupert,  and  extending  from  the  north  and  east  into  eastern  New 


130  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

York  to  form  a  broad  band  in  that  State,  is  a  belt  of  rocks  known 
over  much  of  its  length  of  70  miles  or  more  as  the  "roofing  slate 
belt."  Over  a  distance  of  40  to  50  miles  the  rock  of  this  belt  is 
extensively  quarried  for  roofing  slate. 

At  the  northern  end  of  the  Taconic  range  in  Sudbury,  arena- 
ceous slates  and  phyllites  which  have  been  described  as  Cambrian 
occur  in  close  association  with  masses  of  heavy  quartzite  and 
again  in  proximity  to  other  phyllitic  rocks  which  have  been  de- 
scribed as  of  probably  Ordovician  age.  South  of  Hubbardton 
near  the  western  boundary  of  the  State  and  across  the  line  in 
New  York  have  been  described  large  areas  of  slate  of  probably 
Lower  Cambrian  age,  as  determined  by  fossils  in  associated  lime- 
stones, interspersed  in  no  regular  way  with  slates  and  other  rocks 
which  have  been  described  as  of  Ordovician  age  on  the  basis  of 
graptolites  found  in  the  slates,  and  apparently  sometimes  from 
associated  limestones  and  other  field  relations.  Lower  Cambrian 
fossils  are  reported  widely  distributed  among  the  rocks  of  the 
slate  belt  and  numerous  localities  yielding  graptolites  have  been 
found. 

The  structural  relations  of  the  rock  masses  yielding  these 
different  fossils  are  still  mooted  problems. 

In  1888  Walcott  published  a  preliminary  map  of  this  region. 
In  1891  he  correlated  the  Cambrian  slates  of  this  belt  with  those 
of  Georgia,  Vt.  In  1899  T.  N.  Dale  published  a  revision  of 
Walcott's  map  and  added  many  additional  fossil  localities  to  those 
which  had  been  reported  by  Walcott. 

As  described  by  Dale  the  members  of  the  slate  belt  are  as 
follows : 

Cambrian. 

a.  Olive  grit  (a  graywacke),  more  or  less  massive,  some- 
times with  small  quartzite  beds.  Has  associated  with  it,  in 
places,  a  bed  of  quartzite  12  to  55  feet  thick. 

b.  Roofing  slates,  grayish  green,  purple,  or  mixed  green  and 
purple,  alternating  with  beds  of  calcareous  quartzite  (5  feet)  and 
limestone  breccia  up  to  40  feet  thick. 

c.  Dark  gray  grit,  or  sandstone,  with  shaly  patches. 

d.  Black  shales  or  slates  with  thin  beds  of  limestone  breccia. 

e.  Quartzite  usually  with  spots  of  limonite,  with  some  varia- 
tions and  sometimes  associated  with  a  quartz  conglomerate. 

Ordovician. 

a.  Gray  or  black  shales  and  thin-bedded  limestones;  pos- 
sibly intermittent  ("Calciferous"). 

b.  Black  or  gray  shales  and  slates,  sometimes  banded  from 
bedding  ("Hudson  Shales"). 

c.  Greenish  or  black,  more  or  less  quartzose,  shales  and 
slates,  weathering  white  or  whitish  ("Hudson  White  Beds"), 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  131 

d.  Gray  grit  (graywacke)  interbedded  with  black  shales  or 
slates  ("Hudson  Grits"). 

e.  Green  or  dull  reddish  or  purplish  phyllite  with  very  thin 
beds  of  quartzite,  more  frequent  towards  the  east  ("Hudson  Thin 
Quartzite"). 

f.  Red  and  green  roofing  slate  or  shale  ("Hudson  Red  and 
Green  Slate"). 

Limestone  is  also  described  as  occurring  mostly  west  of  the 
slate  belt.  It  is  called  "Trenton,"  and  is  thought  of  as  perhaps 
representing  Trenton,  Chazy  and  Calciferous  (Beekmantown). 
"Berkshire  Schist"  (sericite,  chlorite  and  quartz  schists),  con- 
taining beds  of  greenish  quartzite  up  to  10  feet  and  over  in  thick- 
ness, is  further  described  as  occurring  east  of  the  slate  belt,  and 
is  regarded  as  probably  representing  all  the  above-named  ter- 
rigenous rocks  called  Ordovician,  and  as  including  Lorraine  and 
Utica  horizons. 


Middle  Cambrian. 

Over  most  of  western  Vermont,  so  far  as  records  obtained 
from  present  outcrops  go,  there  is  above  the  Lower  Cambrian  a 
great  absent  interval.  That  later  Cambrian,  and  particularly  Mid- 
dle Cambrian,  may  have  once  been  more  fully  represented  is  in- 
dicated by  the  discovery  of  a  Middle  Cambrian  fauna  within  a 
rock  which  was  designated  as  an  "intraformational  conglomerate." 

This  so-called  intraformational  conglomerate  was  described 
by  G.  E.  Edson  as  formed  of  dark-colored,  fine-grained  limestone ; 
bluish  or  dove-colored  limestone ;  arenaceous  shale,  in  which  in 
some  instances  are  found  nodules  of  pure  limestone  and  enclosed 
water-worn  pieces  of  bluish-colored  slate;  sandstone  resembling 
quartzite;  arenaceous  Hmestone  in  which  the  enclosed  grains  of 
sand  are  dark  thus  giving  the  rock  a  mottled  appearance ;  and  a 
light-colored  limestone.  The  rocks  (fragments)  forming  this  con- 
glomerate vary  in  size  from  small  pieces  to  bowlders  weighing 
many  tons. 

According  to  Edson  this  formation  first  appears  at  the  present 
surface  near  the  north  line  of  Georgia.  Here  its  "brecciated" 
condition  does  not  appear  at  its  best  and  the  rock  has  the  appear- 
ance of  a  massive,  dark-colored,  arenaceous  limestone.  The  out- 
crop is  described  as  continuing  without  a  break  to  the  north  line 
of  Georgia,  but  there  disappears.  It  reappears  northward  in  St. 
Albans.  At  this  place  the  "brecciated"  condition  is  usually  well 
shown  and  the  rock  is  in  places  associated  with  a  shale.  It  ap- 
pears intermittently  northward  to  the  St.  Albans  line  and  passes 
into  the  town  of  Swanton,  in  which  town  it  is  represented  by  the 
shale  with  which  it  is  associated  farther  south.  Northward  the 
conglomerate  appears  again  and  passes  into  Highgate,  to  the  bank 
of  the  Missisquoi  River.  • 


132  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

The  State  Geologist  submitted  specimens  of  the  fossils  found 
in  this  conglomerate  to  Dr.  Walcott,  who  had  in  his  possession 
some  which  he  had  collected  from  the  same  region.  From  a  pre- 
liminary examination  Walcott  thought  the  fossils  Middle  Cam- 
brian. They  showed  a  considerable  range,  but  Paradoxidcs  was 
described  as  occurring  in  the  matrix  which  would  make  this  rock 
actual  Middle  Cambrian  and  an  "interformational  conglomerate." 

As  further  described  by  Edson  a  L.  acuntinata  was  found  in 
a  shale  lying  close  to  the  conglomerate.  In  Swanton  shale  is 
found  on  both  sides  of  the  conglomerate  and  also  "interstratified" 
with  it.  On  the  western  side  shale  passes  under  the  conglomerate 
and  dips  to  the  east.  The  same  fossils  are  described  as  found  in 
the  various  limestones  and  sandstones  as  are  found  in  the  shale 
and  the  matrix  of  the  conglomerate.  From  the  descriptions  it 
appears  that  the  structural  relations  to  other  formations  are  prob- 
lematical. One  may  hazard  the  opinion  that  the  structural  rela- 
tions of  the  rocks  to  each  other  are  also  complicated  and  pos- 
sibly abnormal  in  some  cases.  The  possibility  of  the  so-called 
conglomerate  being  an  autoclastic  needs  to  be  considered. 

Upper  Cambrian. 

On  the  New  York  side  of  Lake  Champlain  an  Upper  Cam- 
brian sandstone  is  widely  present  and  has  been  described  as  rest- 
ing by  depositional  unconformity  on  pre-Cambrian  rocks.  Ex- 
posures occur  around  Port  Henry,  Essex,  Port  Kent,  and  Keese- 
ville.  This  sandstone  forms  a  wide  fringe  along  the  northern 
side  of  the  Adirondack  mass  of  ancient  pre-Cambrian  rocks. 
Professor  Kemp  has  described  small  outliers  back  from  the  lake, 
west  of  Port  Henry.  On  the  west  side  of  the  lake  faulting  is 
common  in  this  sandstone  and  in  some  places  erosion  has  been 
heavy.  This  rock  has  long  been  known  as  the  Potsdam  from  its 
type  locality  at  Potsdam,  St.  Lawrence  County,  N.  Y. 

In  his  descriptions  of  the  exposures  around  Port  Henry, 
Ruedemann  has  indicated  that  what  is  regarded  as  the  base  of 
this  formation  in  this  region  shows  anomalous  features  in  com- 
parison with  localities  in  Clinton  County,  N.  Y.,  and  on  the  north- 
ern side  of  the  Adirondacks,  especially  in  the  slight  development 
of  a  conglomerate  and  in  the  absence  of  red,  hematitic  arkoses, 
and  reaches  the  conclusion  that  near  Port  Henry  the  Potsdam 
format-ion  does  not  attain  the  great  thickness  which  it  has  farther 
north  and  that  the  lower  Potsdam,  and  perhaps  the  upper,  were 
not  as  fully  developed  as  in  Clinton  County. 

East  of  Lake  Champlain  the  outcrops  of  known  Cambrian 
that  have  certainly  and  definitely  been  determined  by  fossils,  ex- 
cept the  "intraformational  conglomerate"  described  above  and 
occasional  small  exposures  to  be  mentioned  beyond,  belong  to 
the  lower  part  of  this  system,  including  the  rocks  along  the  lake 
shore  which  as  has  already  been  mentioned,  can  be  seen  to  rest 
by  overthrust  on  greatly  disturbed  younger  (Ordovician)   rocks. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  133 

In  his  early  studies  in  the  town  of  Highgate,  Walcott  de- 
scribed a  hmestone  conglomerate  in  the  shale  T apparently  repre- 
senting the  rock  discussed  above  under  Middle  Cambrian  and 
later  described  by  Edson;  containing  fragments  of  limestone  van,^- 
ing  in  size  from  pebbles  to  masses  6  feet  in  diameter.  At  that 
time  Dr.  Walcott  thought  the  fossils  to  have  an  Upper  Cambrian 
aspect.  In  his  later  examination  of  specimens  submitted  to  him 
by  the  State  Geologist  and  in  a  re-examination  of  his  own  material 
he  gave  the  forms  a  wide  range,  although  inclined  to  concede  a 
Middle  Cambrian  age  for  the  matrix  of  the  conglomerate,  if 
Paradoxides  occurred  in  it  (see  above,  page  129 j. 

A  somewhat  siliceous  and  magnesian  limestone,  associated 
with  a  thick-bedded,  barren,  dolomitic  series  that  stratigraphically 
lies  above  it,  is  known  in  southeastern  Xew  York  State,  and  in 
its  exposures  near  Poughkeepsie  in  Dutchess  County,  in  the  Wap- 
pinger  CBarnegat;  limestone,  was  first  described  by  W.  E. 
Dwight  and  later  further  discussed  and  described  by  the  writer. 
Fossils  were  found  by  both  observers,  consisting  of  brachiopods, 
(Lingulepsis  pinnaformis,  and  others  according  to  Dwight;  and 
of  trilobites,  (Ptychoparia,  of  species  found  by  Walcott  at  Sara- 
toga;. These  fossils  were  considered  to  mark  the  rock  as  of 
"Potsdam"  age.  The  region  w^as  mapped  by  the  writer  and  the 
fossiliferous  rock  just  described  was  found  to  pitch  southward, 
in  what  was  called  the  western  strip  of  the  Wap>pinger  belt, 
beneath  the  thick-bedded,  barren  dolomite  which  was  regarded  as 
perhaps  forming  in  part  the  upper  portion  of  the  Cambrian  of  the 
region  and  as  older  than  other  strata  of  "Calciferous"  TBeekman- 
town)  age  lying  above  the  Potsdam  along  the  so-called  "central 
strip"  of  the  Wappinger  belt  as  shown  near  Rochdale,  a  hamlet 
just  northeast  of  Poughkeep>sie. 

The  fossiliferous  limestone  in  Dutchess  County,  assigned  to 
the  "Potsdam"  by  Dwight  and  Gordon,  Walcott  correlated  with  a 
rock,  carrying  similar  fossils,  which  he  had  described  as  occurring 
at  Saratoga.  He  has  called  the  horizon  the  'Totsdam-Hoyt  Lime- 
stone," and  is  inclined  to  place  it  in  the  Upper  Cambrian.  There 
is  some  resemblance  lithologically  between  the  rocks  of  the  two 
localities  thus  correlated,  particularly  betsveen  certain  gray,  arena- 
ceous beds  carr}dng  blackish  streaks  and  patches. 

Messrs.  Brainerd  and  Seely  in  a  paper  entitled  "The  Cal- 
ciferous Formation  in  the  Champlain  Valley,"  wrote  with  much 
positiveness  of  an  Upper  Cambrian  T Potsdam;  horizon,  repre- 
sented by  a  sandstone  and  a  magnesian  limestone  directly  beneath 
other  beds  which  they  called  Eeekmantown.  The  line  between 
the  "Potsdam"  and  the  Beekmantown  was  drawn  just  above 
certain  strata  in  which  brachiopods  related  to  Lingula  were 
found. 


134  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

In  the  writer's  studies  in  Vermont,  in  the  towns  of  Shoreham, 
Orwell  and  Benson,  following  in  some  places  in  the  steps  of 
Brainerd  and  Seely,  these  so-called  "Potsdam"  rocks  were  ex- 
amined and  their  lithological  similarities  in  some  places  with  the 
Dutchess  County  strata,  familiar  to  the  writer,  were  noted.  But 
what  was  more  striking  was  the  aspect  of  similar  deformation  in 
both  cases.  The  characters  of  the  Vermont  rocks  just  mentioned 
will  be  further  discussed  beyond. 

Mr.  Wing  argued  for  the  presence  of  the  Potsdam  beneath 
the  Calciferous  in  Addison  County,  in  his  descriptions  of  the 
sections  near  Shoreham,  and  gave  practically  the  same  account 
of  the  rocks  as  that  furnished  later  by  Brainerd  and  Seely.  Mr. 
Wing  also  apparently,  like  a  great  many  other  observers  of  his 
time,  regarded  certain  rocks  that  are  now  more  generally  looked 
upon  as  Lower  Cambrian  as  belonging  to  the  Potsdam. 

In  December,  1889,  Walcott  announced  the  discovery  during 
the  preceding  summer  of  a  small  outcrop  of  Potsdam  sandstone 
at  Phillipsburg,  Canada,  on  the  east  side  of  Lake  Champlain, 
along  the  shore  of  Missisquoi  Bay,  and  just  north  of  the  Vermont 
border.  .  It  was  described  as  carrying  characteristic  fossils  and 
as  lying  subjacent  to  limestone  of  the  Beekmantown  terrane.  At 
the  same  time  he  mentioned  the  discovery  during  the  same  season 
in  the  lighter-colored  members  of  limestone  at  Point  Levis, 
Quebec,  of  numerous  fossils  of  Upper  Cambrian  or  "Potsdam" 
age. 

In  1889  Ells  described  among  several  distinct  zones  of  con- 
glomerate present  in  the  vicinity  of  Quebec,  one  at  Point  Levis 
interstratified  in  the  fossiliferous  shales  of  the  Levis  Formation 
and  which  contained  a  mixed  fauna.  Some  of  the  pebbles  held 
an  abundance  of  "Potsdam"  forms,  while  the  paste  of  the  con- 
glomerate contained  fossils  characteristic  of  the  Beekmantown 
formation.  He  further  described  a  series  consisting  of  red  and 
green  shales,  green  and  gray  sandstones,  and  beds  of  limestone 
which  represents  what  was  formerly  called  the  "Sillery  and 
Lauzon"  of  the  "Quebec  Group"  of  Logan.  He  considered  the 
series  to  be  of  Upper  Cambrian  age. 

On  the  Montreal  Sheet,  Eastern  Townships  map.  Province  of 
Quebec,  to  accompany  Part  J,  Vol.  VII,  new  series,  Geol.  Sur.  of 
Canada,  a  large  area,  beginning  about  15  miles  north  of  the  Ver- 
mont boundary  and  extending  from  Brigham  Junction  north- 
northeast  to  the  boundary  of  the  map,  is  shown  as  probable  Upper 
Cambrian.  The  rocks  are  red  and  green  shales  with  sandstones 
and  grits,  and  belong  to  the  upper  part  of  the  Sillery  of  the  Quebec 
Group. 

In  western  Quebec  and  eastern  Ontario  the  Potsdam  sand- 
stone appears  to  pass  without  a  break  into  the  overlying  Beek- 
mantown. The  lithological  dissimilarity  between  the  Potsdam  of 
western  Quebec  and  the  supposed  Upper  Cambrian  of  the  eastern 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST,  135 

townships  is  very  striking  and  is  supposed  to  have  been  due  to 
different  conditions  of  deposition.  The  lower  part  of  the  Sillery 
is  said  to  be  undoubtedly  Cambrian  and  to  carry  characteristic 
fossils  {Agnostus,  etc.). 

Some  of  the  rocks  bordering  the  Sutton  Mountain  anticline  in 
Quebec  have  also  been  thought  to  be  Upper  Cambrian;  but  the' 
basal  portion  of  these  rocks  was  thought  to  be  the  equivalent  of 
the  Georgia  series  of  Vermont  and  thought  to  lie  on  "Huronian." 

It  is  now  known  that  the  conglomerate  beds  in  the  Levis 
Formation  carry  in  their  pebbles  Lower  Cambrian,  Upper  Cam- 
brian (or  Lower  Ordovician)  and  Beekmantown  fossils. 

Ulrich  has  created  and  defined  a  new  period  and  system 
under  the  name  '''Ozarkian,"  based  on  sections  in  Missouri,  Ar- 
kansas and  the  southern  Appalachians,  which  is  made  to  inter- 
vene between  the  true  "Upper  Cambrian"  and  the  basal  Ordovician 
(Canadian).  In  this  system  he  places  the  New  York  formations 
known  as  the  Hoyt  Limestone,  the  Potsdam  Sandstone,  the  Little 
Falls  Dolomite,  and  certain  "passage  beds"  first  described  by 
Cushing  from  Jefferson  County,  N.  Y.,  and  called  the  "Theresa 
Formation." 

Schuchert  adopted  the  term  Ozarkian  (1909),  but  used  it  in 
a  different  sense  from  that  of  Ulrich  and  made  it  synonymous 
with  Upper  Cambrian,  or  "Cambric"  in  a  restricted  sense. 

Schuchert  has  referred  certain  conglomerates  of  the  "Quebec 
Series,"  whose  fossils  have  been  described  by  Walcott,  to  the 
"Ozarkian,"  as  he  employed  the  term.  The  formation  from 
which  the  conglomerate  pebbles  came  is  not  known  in  the  St. 
Lawrence  valley. 

Schuchert  would  also  put  Brainerd  and  Seely's  divisions  A 
and  B  of  their  so-called  Beekmantown,  and  apparently  their  so- 
called  Potsdam  also,  as  described  for  Shoreham,  in  the  "Ozark- 
ian," as  Ulrich  would  also,  but  with  a  different  general  significa- 
tion for  the  term. 

It  is  not  fully  settled  whether  any  true  Potsdam,  and  how 
much  that  may  properly  be  called  Upper  Cambrian,  can  be  dis- 
tinguished with  certainty  in  western  Vermont. 

OEDOVICIAIf. 

Beekmantown  (Calciferous), 

The  Vermont  report  shows  this  formation,  as  traced  on  a 
lithological  basis,  as  rather  limited  exposures  in  the  western 
parts  of  Addison  County  and  in  the  northwestern  part  of  Rutland 
County.  The  thickness  is  described  as  about  300  feet.  The 
large  areas  of  limestone  lying  to  the  east  in  Addison  County  and 
northern  Rutland  County  were  called  by  the  special  name  of  the 
"Eolian  Limestone." 

Mr.  Wing  first  described  Calciferous  fossils  from  this  "Eolian 
Limestone"  and  is  reported  to  have  found  them  in  the  Otter  Creek 


136  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Valley  at  New  Haven,  Middlebury,  Salisbury,  Leicester  and  Bran- 
don, on  the  east  side  of  the  stream,  and  in  Weybridge,  western 
Cornwall  and  Shoreham,  on  the  west  side  of  the  creek.  Mr. 
Wing  also  thought  the  Calciferous  to  occur  half  way  between 
Rutland  and  West  Rutland,  and  also  farther  south. 

Brainerd  and  Seely  studied  this  formation  particularly  in 
the  Champlain  valley  and  with  great  industry  examined  "every 
important  exposure  on  the  Vermont  side  of  Lake  Champlain 
from  PhilHpsburg,  Canada,  to  Benson,  Vermont,  and  most  of 
those  on  the  New  York  side."  From  the  sequence  exhibited  at 
Shoreham  they  estimated  the  entire  thickness  as  about  1,800  feet. 
The  formation  was  described  as  showing  a  variety  of  rock  and 
in  some  beds  an  abundant  fauna.  Partly  on  the  basis  of  lithology 
and  partly  by  fossils  the  Beekmantown  was  separated  into  divi- 
sions known  as  A,  B,  C.  D,  and  E,  and  described  somewhat  as 
follows   (descriptions  abbreviated)  : 

1.  Dark,  iron-gray,  magnesian  limestone,  more  or  less 
siliceous,  often  almost  a  sandstone,  in  beds  usually  1  to  2  feet 
thick.     Div.  A,  310  feet. 

2.  Dove-colored  limestone,  intermingled  with  light  gray 
dolomite,  in  massive  beds.     Div.  B,  295  feet.       ' 

3.  Gray,  thin-bedded,  fine-grained,  calciferous  sandstone ; 
followed  by  thick  beds  of  magnesian  limestone;  then  sandstone, 
sometimes  pure,  but  usually  calciferous  or  dolomitic;  magnesian 
limestone  containing  masses  of  chert.     Div.  C,  total  350  feet. 

4.  Blue  limestone  in  beds  1  to  2  feet  thick ;  drab  and  brown 
magnesian  limestone ;  sandy  limestone  in  thin  beds ;  blue  lime- 
stone in  thin  beds  separated  from  each  other  by  thin,  tough,  slaty 
layers,  often  with  conglomeratic  appearance  in  the  presence  of 
small,  angular  pebbles.     Div.  D,  total  375  feet. 

5.  Fine-grained,  magnesian  limestone  in  beds  1  to  2  feet 
thick,  weathering  drab,  yellowish  or  brown.     Div.  E,  470  feet. 

From  PhilHpsburg,  Quebec,  a  series  extends  into  Vermont 
for  four  or  five  miles  in  which  Brainerd  and  Seely  found  beds 
lithologically  similar  to  all  the  above-described  divisions,  although 
division  E  seemed  "poorly  represented"  at  the  north.  The  Phil- 
lipsburg  series  was  classed  by  Logan  in  his  "Quebec  Group," 
under  his  divisions  A  and  B. 

Beekmantown  strata  are  described  for  many  somewhat  scat- 
tered localities  along  the  lake  shore  and  among  the  islands.  The 
series  as  a  whole,  and  the  different  divisions,  are  variously  rep- 
resented at  the  present  surface  in  the  different  exposures  of  this 
formation.  At  Shoreham  the  apparent  thickness  is  great  and 
the  formation  is  well  represented  in  Orwell  township  and  in  ad- 
jacent portions  of  New  York  State. 

An  assemblage  of  remarkable  fossils  was  early  discovered 
at  Fort  Cassin.  The  collections  which  were  made  here  by  Pro- 
fessors  H.   M.   Seely  and   George   H.    Perkins   were   described 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  I37 

chiefly  by  Whitfield  and  became  known  as  the  "Fort  Cassin 
Fauna."  Through  the  stratigraphic  work  of  Brainerd  at  Ball's 
Bay,  according  to  Seely,  this  fauna  was  finally  assigned  to  the 
upper  part  of  division  D.  Representatives  of  the  fauna  were 
also  found  at  a  few  other  places,  as  at  Stave  and  Providence 
islands  (near  Grand  Isle),  at  Valcour  Island  (Van  Ingen  and 
Ruedemann),  and  at  Phillipsburg  (Billings)  ;  but  nowhere  in 
the  abundance  and  fine  condition  of  preservation  as  at  Fort 
Cassin. 

The  Beekmantown  shows  a  small  exposure  on  Grand  Isle 
and  is  present  at  the  southern  end  of  Isle  La  Motte  and  in  both 
places  has  been  mapped  by  Professor  Perkins.  Brainerd  and 
Seely,  and  later  Gushing  and  Ruedemann,  identified  the  several 
divisions  described  for  Shoreham  on  the  west  side  of  the  lake 
by  means  of  similar  lithologic  characters. 

The  Vermont  report  shows  a  wide  band  of  calciferous  rock 
(called  "Eolian")  extending  from  Milton  southward  through 
Charlotte  and  Hinesburgh  into  Monkton.  The  rock  is  predom- 
inantly calcareous,  but  usually  somewhat  siliceous.  Its  precise 
age  has  proved  difficult  to  assign.  Professor  Perkins  classifies  it 
tentatively  with  the  Beekmantown,  although  suggesting  that  part 
of  it  may  be  Cambrian.  In  Colchester,  Mr.  Dan  B.  Griffin,  as- 
sistant to  the  Survey,  has  found  fossils  {"Pleurotomaria"  and 
"Cryptosoon")  and  the  State  Geologist  is  inclined  to  think  that 
this  band  is  largely  if  not  wholly  Beekmantown. 

The  localities  in  Salisbury,  Leicester  and  Brandon  at  which 
Wing  reported  Beekmantown  (Calciferous)  fossils  were  described 
by  him  as  occurring  west  of  the  marble  belt,  and  as  belonging  to 
the  upper  part  of  the  Beekmantown  terrane  ("'Ophileta  beds"). 
Following  the  stratigraphy  of  that  time,  the  quartzite  lying  along 
the  eastern  border  of  the  valley  being  regarded  as  Potsdam,  the 
limestone  which  lies  directly  west  of  it,  "half  way  from  Rutland 
to  the  West  Rutland  valley,"  was  supposed  to  be  Upper  Cal- 
ciferous ("Ophileta  beds"),  but  no  fossils  were  found. 

The  extent  of  the  Beekmantown  formation  in  Addison 
County,  and  along  both  sides  of  the  lake,  its  northern  extension 
into  western  Quebec,  its  representation  southward  in  eastern  New 
York  State,  and  even  farther  south,  so  impressed  Seely  that  he 
wrote:  "and  when  all  the  geological  facts  are  in,  will  it  not  be 
found  that  the  valley  quarries  of  limestone  and  masses  of  marble, 
those  early  known  as  Stockbridge  and  later  as  Rutland,  are 
largely  comprehended  in  the  Beekmantown  ?" 

The  calciferous  rock  lying  to  the  east  of  the  marble  belt  in 
Sahsbury,  Leicester  and  Brandon,  and  southward  through  the 
Vermont  valley,  and  which  borders  the  Lower  Cambrian  quartzite 
of  the  plateau  on  the  west  and  is  associated  with  the  quartzite  of 
the  valley,  has  been  described  as  a  part  of  the  Lower  Cambrian 
series.     See  above.     On  the  map  to   accompany  his  paper  on 


138  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

"The  Commercial  Marbles  of  Vermont,"  Dale  calls  this  somewhat 
regular  belt  of  dolomitic  rocks  "Cambrian  Dolomite."  He  draws 
a  distinction  only  between  this  formation  and  the  marble,  although 
he  includes  some  dolomite  with  the  latter.  In  the  legend  he  calls 
the  whole  limestone  formation  of  the  valley  "Cambro-Ordo- 
vician."  In  the  text  he  writes :  "The  marble  has  been  shown  by 
Wing  and  others  to  include  beds  of  Chazy  age  and  probably  some 
of  Trenton  age  above  them  and  possibly  some  Beekmantown 
below  them.  There  is,  however,  a  question  whether  any  or  how 
much  of  the  dolomite  is  of  Beekmantown  age.  As  this  formation 
along  Lake  Champlain  is  largely  dolomitic  it  would  naturally  be 
sought  among  the  dolomite  beds  of  the  Vermont  valley." 

In  the  present  state  of  knowledge  the  assignment  of  any 
portions  of  the  limestone  of  the  Vermont  valley  to  the  Beekman- 
town is  conjectural  and  provisional. 

Dale  has  described  a  number  of  localities  in  the  slate  belt 
which  exhibit  certain  dark-gray,  calcareous  or  very  quartzose, 
finely-bedded  shales  or  black  shales  with  thin  limestone  beds. 
These  rocks  are  described  as  inconspicuous  and  easily  overlooked. 
They  are  of  inconsiderable  thickness,  and  are  further  characterized 
by  extremely  fine  bedding  and  a  graptolite  fauna.  These  features 
serve  to  distinguish  them  from  adjacent  rocks.  While  some  of 
the  fossils  have  a  range  outside  the  Calciferous  (Beekmantown), 
several  of  them  are  regarded  as  probably  of  Calciferous  age.  It 
is  uncertain  whether  the  horizon  is  everywhere  present  or  only 
intermittent. 

In  eastern  Quebec  is  so-called  Calciferous  (Levis  Forma- 
tion) which  is  very  different  lithologically  from  the  Beekmantown 
described  from  western  Quebec,  Ontario,  Vermont,  and  eastern 
New  York.  It  consists  of  black,  gray  and  green  shales,  and  beds 
of  dolomites,  sandstones  and  conglomerates,  the  latter  carrying 
Cambrian  fossils  (Walcott).  As  explained  on  the  map  to  ac- 
company Part  J,  Vol.  VII,  new  series,  Montreal  Sheet,  Eastern 
Townships,  the  Levis  is  supposed  to  be  the  age  equivalent  of  the 
western  Quebec  Beekmantown  and  the  differences  in  lithology  as 
due  to  different  conditions  of  deposition.  The  Levis  shales  carry 
a  very  different  fauna  from  the  western  Beekmantown.  The 
fossils  are  graptolites  which  were  correlated  by  Lapworth  with 
Arenig  (basal  Ordovician)  of  England.  This  correlation  is  said 
to  ally  the  Levis  fauna  with  a  different  faunal  realm  from  that 
of  the  Beekmantown  of  the  lake  region,  the  latter  being  the  east- 
ern extension  of  a  "Pacific  realm"  fauna  which  was  prevented 
from  interminghng  with  the  eastern  European  fauna  represented 
by  the  Levis  by  a  land  barrier  which  separated  the  "Levis  trough" 
on  the  east  from  a  more  western  "Chazy  trough"  on  the  other 
side  of  the  Green  Mountain  axis. 

As  explained  in  the  discussion  of  the  Upper  Cambrian, 
Schuchert,  and  Ulrich  by  implication,  place  the  lower  portion  of 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  139 

Brainerd  and  Seely's  Beekmantown  in  the  "Ozarkian,"  which 
Schuchert  makes  Upper  Cambrian  and  which  Ulrich  regards  as 
a  separate  system,  belonging  to  the  basal  Ordovician. 

It  has  been  suggested  that  the  upper  part  of  Brainerd  and 
Seely's  Beekmantown  is  probably  more  closely  allied  with  the 
Chazy. 

Chazy. 

In  the  Vermont  report  the  Chazy  was  grouped  with  Birds- 
eye  (Lowville)  and  Black  River,  which  together  were  shown 
forming  a  strip  about  five  miles  wide  narrowing  north  and  south, 
along  the  shore  of  Lake  Champlain  in  Addison  County.  Other 
strips  were  shown  on  Grand  Isle  and  Isle  La  Motte. 

First  Wing  and  later  Brainerd  and  Seely  extended  our  knowl- 
edge of  the  occurrence  and  distribution  of  the  Chazy  rocks. 

Wing  found  the  Chazy  well  represented  by  fossils  at  West 
Rutland  in  the  "Eolian  Limestone,"  and  reported  other  fossils 
from  Leicester,  East  Cornwall  and  Middlebury. 

On  a  map  to  accompany  a  paper  entitled  "Preliminary  Report 
of  the  Geology  of  Addison  County,"  Seely  later  showed  no  Chazy 
in  Addison  County  east  of  the  eastern  boundaries  of  the  towns 
of  Addison,  Bridport  and  Shoreham.  On  page  308  of  the  paper 
he  wrote :  "The  deposits  at  the  lime  quarries  near  Leicester 
Junction  have  been  regarded  as  massive  Chazy  and  yet  the  struc- 
ture approaches  the  Beekmantown.  As  Beekmantown  it  may 
remain  until  new  light  is  thrown  upon  the  obscure  problem." 

Wing  described  a  "striped  stratum"  which  was  regarded  as 
a  marked  feature  of  the  Chazy,  "by  which  the  rock  may  be  recog- 
nized without  its  fossils."  This  was  found  in  Middlebury,  in 
northern  Salisbury,  in  the  western  part  of  Brandon,  and  in  west- 
ern Pittsford.  This  stratum  "doubtless  reaches  the  marble  quar- 
ries of  West  Rutland  and  continues  southward  through  Tinmouth 
and  the  whole  State." 

Chazy  fossils  were  also  reported  by  Wing  from  West  Corn- 
wall, North  Cornwall,  Orwell,  Weybridge  Upper  Falls  and  near 
Bristol  village. 

In  1891  Brainerd  described  sections  at  Valcour  Island,  Crown 
Point  and  Chazy,  N.  Y.  and  also  at  Isle  La  Motte,  Cornwall, 
Orwell  and  Highgate,  Vt.,  and  at  St.  Armand,  Quebec.  At 
Valcour  Island  890  feet  of  Chazy  were  measured  and  separated 
into  divisions  de^gnated  as  A,  B  and  C,  corresponding  to  Lower, 
Middle  and  Upper  Chazy. 

,  ,  The  distinction  among  the  diiTerent  divisions  of  the  Chazy 
was  made  on  the  basis  of  fossils  and  lithology.  The  lower  and 
upper  boundaries  of  the  formation  were  ultimately  established 
and  when  all  the  lower  members  are  present  it  has  now  for  its 
recognized  base  a  ferruginous  sandstone  which  is  prominently 
developed  at  Isle  La  Motte  and  is  known  as  the  "Isle  La  Motte 
sandstone."     It  carries  Lingula  limitaris,  Seely,  as  a  character- 


140  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

istic  fossil.  This  sandstone  rests,  according  to  Seely,  upon  dif- 
ferent members  of  division  E  of  the  Beekmantown,  but  usually 
upon  the  upper  ferruginous  limestone  of  that  division.  The  upper 
strata  of  the  Chazy,  though  varying  somewhat,  bear  most,  often 
a  tough,  magnesian  limestone,  destitute  of  fossils,  and  weathering 
with  an  iron  stain,  while  just  above  is  a  layer  of  flinty  sandstone. 
At  Valcour  Island  the  Chazy  is  described  as  follows  (abbre- 
viated) : 

1.  Gray  or  drab-colored  sandstone,  usually  with  thin  layers 
of  slate  and  with  occasional  thin  layers  of  limestone  at  the  base; 
passing  into  massive  beds  made  up  of  thin,  alternating  layers  of 
tough  slate  and  of  nodular  limestone ;  dark,  bluish-gray,  impure 
limestone  in  beds  of  variable  thickness ;  gray,  tolerably  pure  lime- 
stone in  beds  8  to  20  inches  thick,  separated  by  earthy  seams. 
Lower  Chazy,  Group  A,  338  feet. 

2.  Impure,  nodular  limestone ;  gray,  massive,  pure  lime- 
stone ;  bluish-black,  thick-bedded  limestone,  usually  weathering 
so  as  to  show  pure  nodular  masses  in  a  somewhat  lighter  matrix ; 
dark,  compact,  fine-grained  Hmestone,  with  obscure  bedding; 
bluish-black  limestone.     Middle  Chazy,  Group  B,  350  feet. 

3.  Dove-colored,  compact  limestone  in  massive  beds ;  dark, 
impure  limestone  in  thin  beds ;  tough,  arenaceous,  magnesian 
limestone  passing  into  fine-grained  sandstone.  Upper  Chazy, 
Group  C,  202  feet. 

Like  the  Beekmantown,  the  Chazy  throughout  its  distribu- 
tion at  the  present  surface  shows  some  variations  in  characters 
and  thickness  of  members  and  at  some  places  only  partial  repre- 
sentation of  the  formation. 

In  addition  to  the  localities  given  above,  exposures  of  Chazy 
occur  near  Balls,  MacNeils  and  Merriams  bays,  and  from  Basin 
Harbor  to  Button  Bay,  along  the  east  shore  of  the  lake ;  at  the 
northern  end  of  Providence  Island ;  on  Sawyer's  Island ;  and  on 
Grand  Isle,  where  it  is  represented  somewhat  extensively,  both 
geographically  and  as  a  terrane. 

After  the  discovery  of  characteristic  Chazy  fossils  {Maclu- 
reas)  at  the  surface  in  the  central  and  western  parts  of  the  West 
Rutland  valley  fine,  although  somewhat  distorted,  specimens  were 
found  on  polished  slabs  from  the  bottom  of  the  deep  "Ripley 
quarry." 

South  of  West  Rutland,  in  the  town  of  Ira,  at  Day's  quarry, 
which  was  worked  for  a  time,  Walcott  found  sections  of  large 
gastropods,  probably  Maclureas,  in  a  bluish  marble. 

South  of  West  Rutland  in  the  Vermont  valley  recognizable 
Chazy  fossils,  so  far  as  the  writer  can  determine,  had  not  been 
found  up  to  the  season  of  1920.  See  beyond.  Dr.  Walcott  dis- 
covered fossils  in  the  limestones  south  of  Bennington,  which  were 
assigned  to  the  Chazy-Trenton,  but  no  sharper  distinction  was 
drawn. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  141 

LowTille  (Birdseye). 

In  the  generalized  time-scale  for  eastern  North  America  the 
Lowville  succeeds  the  Chazy. 

An  elevation  at  the  close  of  Beekmantown  time,  accompanied 
by  folding,  in  eastern  North  America,  has  been  described  as 
probable.  This  elevation  is  thought  to  have  raised  much  of  the 
middle  Appalachian  region  and  all  of  New  York  State  except  the 
northeastern  portion  above  water.  In  the  Champlain  region  it  is 
held  existed  a  trough  at  this  time  in  which  was  being  deposited 
the  Chazy.  While  the  Chazy  was  being  deposited  in  the  Cham- 
plain  region  and  in  another  small  (Ottawa)  basin  the  lower 
Stones  River  was  depositing  in  Kentucky  and  Tennessee. 

After  the  deposition  of  the  Chazy  in  the  Champlain  region  it 
is  thought  an  emergence  there  occurred,  forming  land,  which 
was  not  submerged  again  until  the  Black  River  brought  the 
Mississippian  sea  into  the  region.  The  Lowville,  which  is  re- 
garded as  the  time  equivalent  of  the  Upper  Stones  River  of  the 
south,  forms  the  basal  member  of  the  Trenton  series  (Mo- 
hawkian)  in  New  York  and  ushered  in  the  Black  River  inva- 
sion. 

As  mentioned  in  the  discussion  of  the  Chazy  the  Lowville 
was  theoretically  included  with  Chazy  and  Black  River  in  the 
Vermont  report. 

The  Lowville  was  at  first  described  as  very  scantily  repre- 
sented in  Vermont.  Phytopsis  tub'ulosum,  Hall  (a  fossil  which 
has  the  appearance  of  a  bird's  eye  and  which  gave  the  early  name 
to  the  formation),  has  been  seen  only  in  the  northwest  corner 
of  Benson  in  a  bed  about  6  feet  thick.  Elsewhere  this  horizon 
is  described  as  having  only  a  few  feet  of  pure,  fine-grained,  brit- 
tle limestone  with  fine  Hues  of  calcspar,  lighter  in  color  than  the 
known  Black  River  strata  just  above,  and  without  fossils. 

Brainerd  and  Seely  maintain  that  more  than  one  horizon  in 
the  Beekmantown  and  in  the  Chazy  are  lithologically  similar  to 
the  Birdseye,  and  have  been  wrongly  assigned  to  that  formation. 
Assuming  the  rocks  and  fossils  which  had  some  appearance  of 
the  Birdseye  to  belong  to  that  formation  they  sought  localities 
where  the  Chazy  approaches  the  Black  River,  thus  hoping  to 
find  the  Birdseye  between.  But  in  every  locality  so  sought  they 
found  the  Black  River  resting  upon  the  Chazy,  with  no  room  for 
the  Birdseye.  Instead  they  found  the  so-called  Birdseye  in  places 
to  be  underlain  and  overlain  by  members  of  their  Calciferous. 
They  found  fossils  which  have  been  figured  as  sections  of  Phytop- 
sis tubulosum  to  be  "spongoid"  forms,  known  as  Strephochaetus, 
characterizing  their  middle  Chazy.  They  could  find  no  proof 
of  the  Birdseye  in  Vermont,  except  the  small  exposure  in  Benson. 


142  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Black  Eiyer. 

In  their  description  of  the  Beekmantown  of  Vermont,  Brain- 
erd  and  Seely  frequently  refer  to  the  Black  River  as  immediately 
overlying  their  Cliazy.  Northeast  of  Shoreham  village  they 
mention  Black  River,  carrying  characteristic  fossils,  lying  in  a 
trough  of  the  Chazy.  Half  a  mile  south  of  this  exposure  the 
trough  widens  and  the  Trenton  appears  flanked  by  the  Black 
River  and  the  Chazy  in  succession.  Again  in  Orwell,  south  of 
Shoreham,  Black  River  is  described  as  resting  against  the  Chazy, 
the  latter  lying  on  the  former  at  one  place  by  overturn.  Black 
River  is  described  at  Larrabee's  Point,  Thompson's  Point  and 
MacNeils  Bay. 

In  his  paper  dealing  with  the  Chazy  of  the  Champlain  valley, 
Brainerd  describes  and  shows  graphically  in  sections  the  Black 
River  at  Valcour  Island,  Isle  La  Motte  and  Highgate  Springs, 
resting  upon  or  in  close  association  with  Chazy. 

Professor  Perkins  has  mapped  five  separate  exposures  of 
the  Black  River  on  Grand  Isle,  and  one  on  Isle  La  Motte,  and 
refers  to  it  as  occurring  at  Button  Bay  Island  and  at  Benson. 

The  Black  River  strata  are  described  as  fine-grained  lime- 
stone, bluish  at  the  base  and  jet  black  in  upper  layers.  The 
formation  as  a  whole  is  nearly  destitute  of  fossils,  although  some 
thin  layers  are  full  of  them. 

Except  in  the  vicinity  of  Lake  Champlain  the  Black  River 
is  not  positively  known  in  Vermont. 

In  the  Champlain  region  the  Black  River  has  been  thought 
to  lie  disconformably  upon  the  Chazy,  the  latter  having  been 
elevated  and  probably  somewhat  eroded  before  the  Black  River 
invasion. 

Trenton. 

This  formation  as  identified  by  fossils  differs  in  lithology 
and  degree  of  metamorphism  at  different  places.  Some  ter- 
rigenous rocks  by  reason  of  association  with  Trenton  limestone 
or  other  relations  have  been  described  as  probably  of  Trenton 
age. 

The  Vermont  report  shows  the  Trenton  at  Highgate,  on  Isle 
La  Motte,  and  on  Grand  Isle  in  Lake  Champlain;  in  Charlotte 
on  the  lake  shore ;  and  in  the  western  portions  of  Addison  a,nd 
Rutland  counties. 

Mr.  Wing  later  added  details  of  the  Trenton  in  Addison 
County  and  also  found  Trenton  localities  in  the  "Eolian  Lime- 
stone." West  of  or  within  the  slate  belt  of  the  Vermont  report 
he  identified  the  Trenton  at  localities  only  a  few  miles  apart  in 
all  the  towns  north  of  Castleton,  including  Hubbardton,  Sudbury, 
Whiting,  Shoreham,  Cornwall  and  Weybridge ;  and  on  the  east 
of  the  slate  belt'  in  Leicester,  eastern  Cornwall  and  Middlebury. 
The  presence  of  the  Trenton  at  Benson,  south  of  Orwell,  left 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  143 

little  doubt  that  this  formation  exists  "in  long  bands  stretching 
down  on  the  west  of  the  two  belts  of  slate  from  Weybridge 
southward." 

From  the  relations  of  the  "central  slate  belt"  to  the  marbles  in 
Rutland  County  and  farther  south,  Wing  believed  the  Trenton 
abundantly  represented  in  the  marble  belt.  Fossils  (Trinucleus 
concentricus)  were  described  as  found  in  limestones  "interbedded" 
in  the  slates  10  miles  southeast  of  Sudbury,  at  Hubbardton,  and 
a  mile  or  two  north  of  the  slate  quarries  at  West  Castleton. 

In  the  summer  of  1887  Walcott  found  fossils  indicative  of  a 
Trenton  fauna  at  Pownal,  Vt.,  a  mile  north  of  the  Massachusetts 
line,  and  also  on  the  eastern  side  of  Mt.  Anthony  about  3  miles 
south  of  Bennington  Centre. 

In  the  papers  by  Brainerd  and  Seely  on  the  Calciferous  and 
Chazy  of  the  Champlain  valley,  frequent  mention  is  made  of 
Trenton  rocks.  They  are  described  as  forming  a  wide  strip  east 
of  Shoreham,  running  through  Cornwall  and  Whiting  on  the 
west  of  the  "central  slate  belt" ;  also  at  Shoreham ;  at  Orwell ; 
at  Larrabee's  Point;  to  the  east  of  Balls  Bay;  at  Cedar  Branch, 
north  of  MacNeils  Bay;  on  Grand  Isle,  both  inland  and  along 
shore ;  at  Crane  Point,  opposite  Port  Henry,  N.  Y. ;  and  at  Isle 
La  Motte. 

Professor  Perkins  has  shown  wide  exposures  of  this  forma- 
tion on  Grand  Isle  and  has  also  mapped  its  outcrops  on  Isle  La 
Motte. 

Small  exposures  are  mentioned  as  occurring  at  Highgate  and 
St.  Albans,  but  they  are  in  no  cases  extensive.  The  formation  is 
described  as  not  occurring  along  the  lake  shore  north  of  Charlotte, 

Dale  thinks  that  some  of  the  limestones  of  the  marble  belt 
are  of  Trenton  age.  On  his  map  of  the  slate  belt  of  eastern  New 
York  and  western  Vermont,  Ordovician  limestone  is  shown  as 
an  interrupted  band  along  part  of  the  western  border.  In  Benson 
this  limestone,  with  a  few  small  patches  of  slaty  or  gritty  rocks, 
is  represented  as  a  band  2  miles  wide  along  the  shore  of  the  lake. 
Just  east  lies  the  so-called  "Benson  Black  Slate"  over  an  area 
about  2  miles  wide  and  5  miles  long  and  this  is  bounded  on  the 
east  by  an  irregular  strip  of  the  limestone.  These  two  areas  of 
limestone  are  shown  as  separated  at  the  south  from  another  area 
of  the  limestone  about  2^  miles  wide  south  of  West  Haven. 
The  latter  area  narrows  southward,  and  with  only  one  inter- 
ruption, extends  to  West  Granville,  N.  Y.  Fourteen  miles  south 
of  West  Granville  a  narrow  band  runs  from  North  Argyle  to 
Argyle  in  New  York.  In  the  text  these  areas  are  referred  to  as 
the  Trenton  limestone.  Outcrops  are  specially  mentioned  as  oc- 
curring in  Hartford  and  at  Carver's  Falls  in  Poultney  River.  An 
area  is  shown  northwest  of  Hubbardton,  surrounded  by  the  slate, 
phyllite  and  grit  formation.  At  Carver's  Falls  and  at  several 
other  points  near  the  Cambrian  boundary,  with  which  the  lime- 


144  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Stone  is  shown  in  contact  over  long  distances,  according  to  the 
map,  the  Hmestone  yields  Trenton  fossils.  In  several  places  this 
limestone  "may  represent  the  entire  Lower  Silurian  series  and 
should  then  be  regarded  as  Trenton,  Chazy  and  Calciferous." 
The  Trenton  limestone  is  mentioned  as  occurring  sporadically 
within  the  Ordovician  areas  of  the  slate  belt. 

In  general  as  thus  far  described  the  Trenton  formation  is 
calcareous.  Several  observers  have  regarded  limestone  of  this  age 
as  interbedded  with  members  of  the  slate  formation.  Dale  says 
that  the  limestone  was  probably  in  some  places  deposited  con- 
temporaneously with  the  "Hudson"  grits  and  shales.  In  his  table 
and  descriptions  of  formations,  those  designated  as  "Hudson 
grits,  Hudson  red  and  green  slates,  Hudson  thin  quartzite,"  are 
put  in  the  Ordovician  and  in  part  referred  to  or  described  as 
probably  representing  the  Trenton  limestone,  described  above  as 
occurring  west  of  the  slate  belt.  Dale  describes  what  appeared 
to  him  as  indications  of  transition  between  Hudson  grit  and  the 
"Berkshire  Schist"  of  the  Taconic  range,  and  from  the  areal  rela- 
tions infers  that  the  latter  is  equivalent  to  the  entire  Ordovician 
among  the  slates  and  grits  and  in  addition  to  representing  the 
Calciferous,  Chazy  and  Trenton  includes  also  probably  the  Lor- 
raine and  Utica. 

Foerste  describes  Trenton  fossils  as  occurring  in  thin  blue 
limestone  which  forms  intercalated  bands  in  the  base  of  the  slate 
formation.  He  gives  'two  localities  near  Danby  Four  Corners, 
12  miles  south  of  Rutland,  and  another  on  the  ridge  west  of 
Otter  Creek  a  little  northwest  of  South  Wallingford.  He  men- 
tions branching  bryozoa,  crinoid  beads,  and  sections  of  Stropho- 
mena  and  Streptelasma. 

IVormanskill. 

Graptolite  shales  "interbedded  or  associated"  with  "Hudson" 
grits  in  the  slate  belt  are  assigned  to  the  Normanskill  Zone 
(Trenton)  by  Dale. 

Utica. 

The  so-called  "Utica"  has  a  wide  distribution  in  the  region 
of  the  lake.  The  Vermont  report,  which  separates  this  forma- 
tion from  the  "Hudson  River,"  shows  the  Utica  as  forming 
Alburgh  peninsula,  North  Hero  and  much  of  Grand  Isle,  and  on 
the  mainland  of  Vermont  further  indicates  a  strip  extending  from 
the  shore  of  Missisquoi  Bay  southward  through  Highgate  and 
Swanton  to  St.  Albans  Bay ;  again  at  the  mouth  of  the  Winooski 
River  and  from  Charlotte  on  the  east  of  the  Trenton  limestone 
south  to  Shoreham.  It  is  described  as  pjnching  out  in  Orwell 
near  "Chittenden's  Mills."  A  narrow  strip  is  shown  skirting  the 
lake  on  the  west  of  the  Trenton  in  Addison  County,  and  a  small 
patch  on  the  lake  west  of  Bridport. 

According  to  Professor  Perkins  what  was  mapped  by  the 
Vermont  Survey  as  "Hudson  River"  is  also  Utica.     According 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  145 

to  Perkins :  "Here  and  there  the  Utica  appears  on  the  Vermont 
shore  of  Lake  Champlain  and  in  small  patches  away  from  the 
lake."  Juniper  Island,  the  Four  Brothers  and  Rock  Dunder 
in  the  lake  are  also  formed  of  Utica  slate. 

Mr.  Wing's  investigations  apparently  dealt  chiefly  with  the 
Hmestone  formation  ("Eolian"),  and  only  indirectly  with  the 
slate.  The  slate  of  the  great  "central  slate  belt"  of  the  Vermont 
report  he  called  "Hudson  River"  and  showed  it  in  sections  and 
discussed  it  as  conformably  overlying  the  Trenton  formation. 
At  West  Rutland  "the  Chazy  adjoins  the  slate  belt."  The  lime- 
stones containing  Trenton  fossils  "over  the  interior"  of  the  slate 
belt  had  the  appearance  of  being  "brought  up  from  beneath  by 
anticlinals." 

Brainerd  and  Seely  maintained  that  all  the  rocks  of  the 
Lower  Silurian  appear  on  the  Vermont  side  of  Lake  Champlain, 
sometimes  showing  in  their  natural  order  in  great  monoclinals 
with  Utica  slate  at  the  top,  lying  on  the  Trenton  limestone.  They 
made  the  slate  of  the  "central  slate  belt"  which  Wing  called 
"Hudson  River"  in  the  Shoreham  section,  of  Utica  age,  thus  cor- 
relating it  with  the  slate  formation  lying  west  of  the  "great  fault," 
or  the  slate  of  the  Lake  Champlain  region  proper.  These  ob- 
servers show  the  Utica  in  faulted  contact  with  the  Chazy  and 
Trenton  at  Isle  La  Motte.  Professor  Perkins  shows  the  Utica 
widely  distributed  on  Grand  Isle,  forming  the  larger  part  of  the 
island;  also  three  patches  along  the  east  shore  of  Isle  La  Motte. 

Within  the  roofing  slate  belt  the  Utica  is  not  distinguished. 
East  of  the  slate  belt  the  Berkshire  Schist  is  made  probably  to 
include  this  horizon. 

On  Grand  Isle  Professor  Perkins  has  described  characteristic 
Trenton  fossils  and  so-called  "Utica"  types  occurring  on  the 
same  slab. 


Later   OrdoYician    ("Lorraine,"   "Hudson   Mirer"). 

The  presence  of  rocks  of  Ordovician  age  younger  than  so- 
called  "Utica"  in  western  Vermont  cannot  be  affirmed  from  the 
rocks  themselves.  Perkins  maintains  that  in  the  Lake  Cham- 
plain region  all  the  slate  formation  is  of  Utica  age  (or  older 
perhaps). 

In  the  Taconic  range  the  Berkshire  Schist  is  made  provi- 
sionally to  include  Lorraine,  and  many  of  the  terrigenous  rocks 
of  the  roofing  slate  belt  are  not  specifically  assigned  beyond  in- 
dicating that  some  of  them  are  probably  equivalent  to  the  Trenton 
(and  the  Calciferous  and  Chazy).  They  are  usually  referred  to 
by  the  non-committal  term  "Hudson,"  which  term  in  its  present 
usage,  includes  Trenton  and  older  and  younger  terranes. 


146  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

GENERAL  STRUCTURAL  CONSIDERATIONS. 

Preliminary  statement.  Throughout  their  length  and  breadth 
in  western  Vermont,  from  the  Canadian  boundary  to  the  Massa- 
chusetts line,  and  in  their  geographical  extensions  into  Quebec  at 
the  north  and  into  Massachusetts  and  New  York  at  the  south  and 
west,  the  formations  just  discussed  present  a  wonderfully  fas- 
cinating field  with  respect  to  the  secondary  deformations  which 
they  have  suffered.  For  a  bold  sweep  of  the  imagination  there 
is  no  aspect  of  Vermont  geology  so  inviting  as  that  of  the  wide- 
spread dislocations  which  have  followed  the  action  of  compres- 
sive stresses  in  the  earth's  crust.  By  these  forces  the  rocks  have 
been  piled  on  each  other  and  shoved  from  east  to  west. 

In  the  Taconic  region  the  deformational  history  is  very 
complicated  and  difficult  to  read.  Many  views  of  the  structure 
have  been  given  and  there  probably  will  always  be  divergence  of 
opinion. 

The  present  erosional  aspects  of  the  region  in  many  par- 
ticulars seem  clearly  to  be  due  to  structure  produced  by  ancient 
processes  of  deformation  and  as  one  studies  the  topography  and 
geology  together  it  becomes  apparent  that  the  physiography  of 
today  had  its  genesis  in  crustal  disturbances  of  a  more  or  less 
remote  past. 

Brief  sum>mary  of  various  studies  that  have  been  made  in 
the  deformation  of  the  earth's  crust  in  various  parts  of  the  world, 
and  of  certain  theoretical  aspects  of  the  subject.  In  their  work 
of  mapping  the  areal  and  structural  relations  of  formations  in 
various  parts  of  Europe  and  of  this  country  during  the  past  forty 
or  more  years,  geologists  have  in  some  cases  readily  come  to 
recognize  and  sometimes  have  been  forced  to  reckon  with  the 
existence  of  great  displacements  of  the  crust  in  order  to  account 
for  the  field  relations  which  certain  regions  show.  Especially 
noteworthy  is  that  class  of  deformations  comprising  overturned 
folds,  shearing,  reverse  faults  and  thrusts. 

All  these  secondary  structural  features  often  share  with  each 
other  the  displacement  changes  of  a  given  region  and  sometimes 
apparently  have  a  common  general  relation  to  a  definite  regional 
deformation.  Uncertainties  will  naturally  arise  concerning  the 
extent  to  which  the  various  secondary  deformations  due  to  com- 
pression, in  a  given  region,  are  related  to  the  same  general  epi- 
sode ;  or,  if  there  is  reason  to  think  that  pressure  acted  intermit- 
tently, as  to  whether  it  acted  in  the  same  direction  at  various 
times.  Evidence  has  been  offered  to  show  that  in  certain  regions 
thrust  movements  have  been  widely  separated  in  time  and  have 
acted  in  practically  diametrically  opposite  directions. 

It  is  usually  not  easy  to  fix  the  precise,  or  even  the  proximate, 
date  for  the  chief  displacement  features  of  a  region,  or  to  appor- 
tion the  various  deformations  therein  among  different  epochs  in 
those  cases  in  which  a  region  is  known  or  suspected  to  have  been 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  147 

affected  by  crustal  movements  more  than  once  and  at  more  or 
less  widely  separated  times.  The  degree  of  probability  rests 
upon  different  conditions  in  different  regions.  In  certain  regions 
where  older  formations  now  rest  by  thrust  on  younger  masses, 
these  relations  by  themselves  may  serve  to  indicate  only  a  general 
limit  of  antiquity  and  other  conditions  may  or  may  not  give  an 
idea  of  the  precise  date  at  which  the  actual  deformation  occurred. 

Sometimes  the  evidence  points  to  the  formation  of  a  major 
thrust  whose  plane  was  subsequently  folded  and  suffered  offsets 
and  other  later  disturbances.  The  latter  may  in  certain  regions 
be  reduced  to  a  type  characteristic  of  later  orogenic  movements 
or  other  displacements  and  serve  to  show  at  least  separate  epi- 
sides  of  disturbance,  while  they  leave  undecided  the  question  of 
how  much  earlier  the  major  thrust  occurred  than  did  those  move- 
ments which  modified  it  in  various  ways. 

In  certain  cases  perhaps  the  existence  of  a  stratum  com- 
petent to  transmit  a  great  lateral  thrust  may  serve  to  indicate  the 
limit  of  antiquity  of  the  movement,  while  the  relations  at  the 
same  time  afford  no  means  of  telling  at  what  time  subsequent  to 
the  formation  of  the  competent  stratum  it  was  called  upon  to 
exercise  its  influence.  The  problem  might  perhaps  be  further 
complicated  in  some  cases  by  the  possible  former  existence  of  a 
competent  stratum  which  had  been  partially  or  wholly  eroded  and 
which  by  reason  of  its  original  relation  to  the  load  which  it 
carried  could  have  initiated  a  thrust  which  was  participated  in 
by  a  lower  stratum,  also  competent  under  proper  conditions, 
which  obtained  relief  by  the  fracture  initiated  by  the  more  super- 
ficial part  of  the  crust,  the  fracture  of  the  latter  changing  the 
relations  between  the  deeper  stratum  and  its  load,  which  had  pre- 
vented fracture  until  the  relief  of  the  initial  fracture  was  felt 
by  it. 

In  some  cases  a  thrust  movement  may  not  have  occurred 
until  erosion  had  so  changed  the  relations  of  a  stiff  stratum  with 
respect  to  its  load  that  it  fractured,  in  which  case  the  thrust 
would  be  thought  of  as  occasioned  by  reason  of  erosion  preceding 
or  assisting  compression.  In  a  case  in  which  erosion  preceding 
any  compression  seemingly  made  possible  a  thrust  movement  and 
in  which  the  erosion  was  apparently  carried  to  a  stage  of  pene- 
planation  prior  to  the  thrust,  the  date  of  the  peneplain,  if  ascer- 
tainable, might  serve  to  fix  the  probable  date  of  thrust. 

In  some  regions  the  fact  of  different  dates  of  compression 
might  be  perceived  by  reason  of  the  difference  in  degree  of  dis- 
placement produced  as,  for  example,  where  it  would  be  possible 
to  associate  one  class  of  fractures  with  the  folding  of  an  earlier 
thrust  of  relatively  large  displacement. 

While  it  is  possible  to  imagine  the  formation  first  of  a  major 
thrust  whose  plane  was  subsequently  disturbed  by  folding  and 
thrusts,  there  are  regions  in  which  the  conditions  seem  clearly 


148  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

to  indicate  that  minor  thrusting  or  reverse  faulting  along  many 
separate  planes  and  apparently  involving  previous  folding,  oc- 
curred first,  piling  the  strata  on  each  other,  sometimes  to 
enormous  thickness,  and  that  a  later  thrust  passed  beneath  the 
whole  and  cut  off  the  whole  series  of  earHer  minor  thrusts  whose 
planes  came  to  lie  at  oblique  angles  with  the  major  thrust  plane. 
More  than  one  series  of  minor  thrusts,  or  reverse  faults,  and  an 
associated  major  thrust  may  exist  in  the  same  region,  which  sug- 
gest different  episodes,  or  periods  of  compression,  for  that  region. 
Moreover,  in  addition  to  these  minor  and  major  thrusts  there 
may  be  one  or  more  later  and  still  more  powerful  or  "maximum" 
thrusts,  so  formed  that  the  later  of  these  override  the  earlier, 
while  all  may  overlap  the  previous  minor  and  major  thrusts  of 
the  region,  at  one  or  more  places.  A  very  complicated  condition 
is  thereby  produced.  The  maximum  thrusts  carry  the  older  rocks 
over  the  younger,  but  with  various  degrees  of  overlapping,  and 
the  overthrusting  may  go  so  far  as  to  carry  the  disturbed  portion 
of  the  crust  over  on  undisturbed  strata.  While  a  common  direc- 
tion of  movement  and  a  sequential  nature  in  these  displacements 
and  therefore  their  relative  dates  might  be  apparent,  the  question 
of  their  geological  dates  might  still  remain  open. 

A  condition  that  might  be  inferred  to  be  due  to  folding  ante- 
cedent to  thrusting  is  frequent  in  such  regions  as  just  described, 
but  it  is  explained,  sometimes  at  least,  as  occasioned  by  friction 
along  the  unyielding  plane  over  which  the  upper  material  moved, 
so  that  there  was  a  tendency  for  the  upper  part  to  curve  under  and 
produce  inversion  of  beds. 

The  outcrops  of  the  maximum  thrust  planes  under  erosion 
resemble  boundary  lines  between  unconformable  formations 
because  of  greater  or  less  discordance  between  the  strata  above 
and  below  the  plane  of  fracture. 

In  regions  of  long-continued  and  profound  erosion  and  in- 
volving at  the  present  surface  very  old  rocks  the  problem  of  the 
dates  of  various  disturbances  may  shift  to  one  of  sheer  uncer- 
tainty, especially  when  a  region  is  known  or  believed  to  have 
been  involved  in  two  or  more  mountain  building  deformations 
and  one  or  more  of  these  disturbances  are  also  known  to  have  been 
a  long  time  subsequent  to  the  dates  of  formation  of  the  rocks 
which  now  lie  in  displaced  relations  to  each  other.  It  is  con- 
ceivable that  a  relatively  recent  orogenic  movement  might  have 
dislocated  and  deformed  a  region  involving  rocks  of  much  greater 
antiquity  than  the  date  of  the  movement  itself  and  give  results 
not  to  be  readily  distinguished  from  those  which  would  have 
followed  a  compression  of  those  rocks  shortly  after  their  forma- 
tion. 

Displacements  have  been  described  in  the  Canadian  Rockies 
in  which  an  original  width  of  50  miles  has  been  shortened  to 
half  that  distance  by  a  succession  of  thrusts  along  a  number  of 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  149 

parallel,  longitudinal  fractures  which  have  produced  a  series  of 
huge  oblong  blocks  resting  on  one  another  from  west  to  east,  and 
apparently  produced  without  much  preliminary  bending.  Over- 
turned folds  were  observed  along  the  courses  of  some  of  the 
faults,  but  were  described  as  usually  small  and  of  minor  structural 
importance.  Violent  folding  in  the  prolongation  of  a  fault  line 
and  undulations  of  major  fault  planes  indicating  disturbance 
subsequent  to  the  main  faulting  were  observed.  In  the  belt  of 
fracture  there  were  recognized  seven  principal  faults  of  varying 
throws.  There  was  observed  a  very  striking  apparent  conformity 
between  beds  zvidely  different  in  age  east  of  the  axis  of  the 
region. 

It  will  appear,  either  in  regions  in  which  strata  belonging 
to  epochs  approximating  in  age  relations  the  date  of  later  defor- 
mations have  never  been  deposited,  or  in  those  in  which  such 
strata  though  deposited  have  been  eroded,  as  though  only  those 
rocks  which  are  now  visible  were  involved ;  but  in  one  case  it 
will  be  necessary  to  recognize  that  a  former  load  may  have  con- 
trolled or  modified  the  action  of  the  deforming  forces.  It  may 
be  that  the  only  Hght  one  may  be  able  to  get  upon  such  a  pos- 
sibility will  come  from  considering  the  whole  general  region,  of 
which  the  province  under  consideration  is  apparently  a  genetic 
part.  Late  Paleozoic  rocks,  for  example,  may  be  much  more 
sparsely  represented  today  in  New  England  than  in  the  past. 
The  conditions  in  neighboring  New  York  and  the  fact  that  we 
are  probably  dealing  with  an  upraised  peneplain  of  a  great  up- 
thrust  segment  of  the  crust  should  perhaps  be  remembered  in 
our  studies  in  western  New  England. 

The  probability  of  difficulty  in  working  out  the  dates  of 
deformations  in  a  region  as  the  result  of  the  fact  that  nature 
works,  at  least  to  some  extent,  with  the  same  rock  masses  at 
separate  epochs  and  under  various  conditions  is  apparent.  Such 
conditions,  in  efforts  to  discriminate  among  the  effects  of  possible 
different  crustal  movements,  will  lead  to  differences  of  interpreta- 
tion almost  surely  where  present  relations  are  greatly  involved. 

In  passing  it  seems  worthy  of  note  that  any  principle  which 
assumes  that  the  minor,  secondary  structural  features  of  a  region 
may  be  taken  as  replicas  of  the  larger  deformations  must  be  used 
with  caution. 

The  problem  of  the  structure  of  a  region  often  involves  as 
primary  conditions  the  nature,  sequence  and  thickness  of  sedi- 
mentary formations  and  the  complex  nature  of  the  substratum  on 
which  these  are  deposited,  such  as  rigidity,  condition  of  previous 
strain,  irregularity  of  surface  and  admixture  of  crystalline 
masses.  It  must  further  reckon  with  antecedent  deformation  of 
any  kind  and  frequently  upon  consequent  strains  in  those  cases 
in  which  the  structural  features  are  of  different  dates.  It  must 
take  account  of  the  possibility  of  variations  in  the  strength  of  the 


150  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

compressive  forces  at  different  times,  or  in  different  parts  of  a 
region  during  the  same  episode ;  of  metamorphism  and  resulting 
crystallization  or  re-crystallization  of  rocks ;  of  erosion  at  dif- 
ferent periods ;  and  of  periods  of  tension  stresses  and  normal 
faulting. 

DESCRIPTION  AND  DISCUSSION  OF  FIELD  STUDIES 
BY  THE  WRITER  IN  WESTERN  VERMONT. 

General  plan  of  discussion.  For  convenience,  general  refer- 
ence to  field  studies  in  this  paper  will  be  given  by  counties  and 
by  towns  which  are  shown  on  the  accompanying  map,  plate  XXII. 
Observations  and  citations  are  based  on  the  topographic,  quad- 
rangle sheets  of  the  United  States  Geological  Survey.  Close 
reference  to  localities  mentioned  will  require  the  use  of  these 
maps.  Some  assistance  may  also  be  had  from  the  map  showing 
physiographic  divisions,  and  from  certain  landmarks  such  as  large 
towns  or  cities,  township  boundaries  and  rivers.  For  the  town- 
ships of  Brandon,  Sudbury  and  Orwell  a  special  map  is  offered, 
Plate  XXII. 

ADDISON  COUJfTT. 
Orwell  Township. 

(Ticonderoga  topographic  sheet.) 

Topography.  The  township  has  a  somewhat  diversified 
topography.  A  spur  of  the  foothills  of  the  Taconic  range  enters 
it  from  the  town  of  Benson  at  the  south.  Over  this  spur  the 
contours  of  600  and  700  feet  run  for  long  distances.  The  high- 
est point  is  1,000  feet.     There  are  several  scarps  within  the  spur. 

This  high  land  extends  nearly  to  the  lake  in  southwestern 
Orwell,  but  the  surface  of  the  northwestern  part  of  the  town  is 
a  gently-rolling  upland  with  contours  at  or  below  the  400  level. 
The  surface  of  East  Creek  over  much  of  its  length  is  practically 
that  of  the  lake.  Along  the  creek  and  the  lake  shore  are  large 
tracts  of  Champlain  clays,  which  effectually  conceal  the  under- 
lying rock. 

East  of  the  spur  described  is  a  valley  through  which  courses 
the  Lemon  Fair  River  and  which  separates  the  spur  from  the 
Sudbury  hills.  This  valley  has  a  minor  ridge  running  in  a 
general  north-south  direction  through  it. 

Mount  Independence.  The  flattish  position  of  the  strata 
forming  this  hill  is  noticeable.  They  dip  about  10°  northerly. 
Forming  the  basal  members  at  the  southern  end  are  thick-bedded, 
whitish,  quartzitic  sandstones  which  Brainerd  and  Seely  called 
"Potsdam"  and  assigned  a  thickness  of  170  feet.  Then  come 
dark-gray,  siliceous  and  magnesian  rocks,  in  some  cases  almost 
quartzites,  and  then  interbedded  dolomites  and  limestones.  The 
rocks  of  the  hill  above  the  so-called  "Potsdam"  were  called  Beek- 


152 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 


mantown  (Calciferous)  by  Brainerd  and  Seely  and  put  in  their 
divisions  A  and  B.  The  writer  did  not  find  along  the  lake  shore 
or  at  any  other  part  of  the  base  of  this  hill  any  contact  with  other 
rocks  than  those  which  make  up  the  hill.  It  seemed  to  be  sur- 
rounded on  the  landward  portion  by  the  Champlain  clays. 


w 


Figure  9.  Section  to  show  interpretation  of  the  relations  at  Mt.  Independence. 
U,  "Utica"  slate ;  P,  "Potsdam"  ;  "A"  and  "B,"  lower  "Beekmantown." 
The  lower  Ordovician  has  been  thrust  on  the  "Utica"  slate  formation. 
A  possible  normal  fault,  F,  is  shown  which  displaced  the  whole  series  at 
the  west,  including  the  thrust  plane.  1-2,  thrust  plane.  S-S,  erosion 
surface  of  the  hard  rock  formations. 

Chipman's  Point.  One  and  a  half  miles  south-southeast  of 
Mt.  Independence  thick  beds  of  dark-gray,  magnesian  limestone 
emerge  from  the  lake  north  of  Chipman's  Landing,  with  general 
northerly  dip  and  strike  of  N.  58°  E.  One-half  mile  southeast 
of  the  landing  these  beds  which  seem  to  have  suffered  no  break 
within  them,  disappear  into  the  lake  with  general  southerly  dip, 
thus  appearing  to  form  a  gentle  arch  with  general  direction  of 
its  axis  east  and  west.  So  far  as  observed  along  shore  these  beds 
are  similar  to  those  lying  above  the  "Potsdam"  in  Mt.  Inde- 
pendence. At  many  places  the  rocks  dip  abruptly  into  the  lake. 
No  so-called  "Potsdam"  was  observed.  Eastward  these  rocks 
pass  beneath  the  clays.  No  contacts  with  other  rocks  were  found. 
The  strata  indicated  only  gentle  deformation  within  them. 

South  of  Chipman's  Point.  South  of  Chipman's  Point  are 
three  promontories  known  by  campers  along  the  shore  as  "The 
Phoebes."  These  are  composed  of  black,  limy  slates  and  shales 
with  bands  of  interbedded  black  hmestone.  All  are  much  dis- 
turbed and  show  not  only  a  highly-inclined  easterly  dip  as  a 
rule,  but  internal  crushing  as  well.  The  shaly  members  of  the 
southern  promontory  gave  Graptolithiis  pristis,  and  bowlders 
of  the  interbedded  limestone  at  the  base  of  the  cliff  yielded 
Plectambonites  sericeus,  Dalmanella  testudinaria,  and  Trinucleus. 

One  hundred  and  fifty  rods  south  of  this  promontory  a  brook 
enters  the  lake.  Slate  outcrops  in  the  bed  a  few  rods  from  the 
shore  and  is  succeeded  up  the  brook  by  a  magnesian  limestone, 
dipping  easterly  and  resembHng  part  of  the  lower  Beekmantown 
of  the  exposures  at  the  north.     In  the  field  northeast  of  this 


KEPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  153 

brook  are  dark,  magnesian  limestones.  In  lithology  and  presence 
of  chert,  some  of  this  rock  resembles  division  A  of  Brainerd  and 
Seely's  Beekmantown.  This  is  succeeded  eastward  by  other 
magnesian  limestone  of  general  gray  color  and  probably  part  of 
the  Beekmantown. 

South  of  this  brook  is  a  hill  known  as  "Blue  Ledge"  by  the 
campers.  The  ledge  shows  an  almost  perpendicular  scarp  from 
150  to  200  feet  above  the  surface  of  the  lake.  The  west  face 
of  the  scarp  to  a  height  of  100  plus  feet  is  composed  of  slate  like 
that  of  "The  Phoebes"  at  the  north.  The  shaly  layers  yielded 
Graptolifhus  pristis.  The  summit  of  the  scarp  and  the  eastern 
slope  of  the  hill  is  a  magnesian  limestone  like  that  in  the  brook 
bed  just  north  and  is  probably  Beekmantown.  The  topography 
shows  that  "Blue  Ledge"  is  bounded  on  the  north  and  south  by 
east-west  faults  of  the  normal  type.  The  limestone  capping  the 
hill  dips  easterly.     See  figure  10. 


Figure  10.  Section  to  show  relations  at  "Blue  Ledge,"  on  the  Orwell  shore 
of  Lake  Champlain.  A,  "Utica"  slate  formation ;  B,  massive  dolomite, 
probably  of  "Beekmantown"  age ;  1-2,  thrust  plane.  Curved  arrow  in- 
dicates folding  of  "Utica"  strata ;  straight  arrow  indicates  bodily  thrust 
of  massive   "Beekmantown"   on  slate  formation. 

South  of  "Blue  Ledge"  is  an  abandoned  farm.  Just  north 
of  the  old  barn  is  an  exposure  of  the  "Utica"  and  not  more  than 
10  yards  to  the  east  of  the  slate  is  a  low  scarp  in  the  dolomite, 
but  the  contact  is  concealed.  These  relations  are  shown  in 
plate  XXIV. 

The  relations  at  "Blue  Ledge"  and  at  the  old  farm  thus  give 
clear  and  unmistakable  evidence  that  the  slate  formation  is  over- 
lain by  the  dolomite  which  is  all  regarded  as  forming  some  part 
of  the  Beekmantown  of  the  region,  on  the  basis  of  the  lithology 
of  the  rock.  The  indication  is  that  "The  Phoebes"  owe  their 
present  topographic  prominence  to  a  protective  covering  of  the 
Beekmantown  which  has  been  removed  at  a  relatively  recent 
epoch.  For  the  Beekmantown  to  have  its  present  position  on  the 
younger  formation  an  overthrust  is  assumed. 

Questions  then  arise  with  reference  to  the  former  exten- 
sion of  the  Beekmantown  in  the  neighborhood.     Is  it  present 


154 


REPORT  OF  THE3  VERMONT  STATE  GEOLOGIST, 


beneath  the  clays  between  Chipman's  Point  and  Mt.  Indepen- 
dence? If  not,  was  it  once  present  there  lying  on  the  slate 
formation  and  did  it  also  once  cover  the  slates  to  the  east  of  the 
lake  shore  over  the  areas  now  largely  concealed  by  clays,  but  in 
which  along  the  various  stream  incisions  the  slates  can  be  seen 
to  form  the  surface  rock?  East  of  these  clays  and  west  of 
Orwell  village,  as  will  presently  be  described,  the  Beekmantown 
occurs  again  and  in  apparent  overthrust  relation  to  the  slates. 
It  therefore  appears  probable  that  these  questions  just  asked  as 
to  a  probable,  former,  widespread  covering  of  the  slates  by 
Beekmantown  may  be  answered  in  the  affirmative. 

The  conditions  at  Mt.  Independence,  at  Chipman's  Point 
and  at  other  places  indicate  gentle  flexures  in  the  dolomite  forma- 
tion; while  those  at  "Blue  Ledge"  and  west  of  Orwell  village 
show  that  the  formation  has  been  fractured.  It  appears  prob- 
able that  certain  structural  features  permitted  the  removal  of 
Beekmantown  beds  over  the  areas  intervening  among  its  present 
surface  outcrops  and  that  Mt.  Independence,  and  perhaps  also 
the  dolomite  at  Chipman's  Point,  are  thrust-erosion  inhers  in  the 
slate  formation.  On  the  whole  it  appears  probable  that  the 
present  exposures  of  the  dolomite  are  the  downthrow  portions 
of  the  formation  as  deformed  by  normal  faulting  and  that  many 
of  the  flexures  which  the  formation  shows  are  products  of  the 
same  deformation. 


Figure  11.  Generalized  section  to  show  interpretation  of  relations  along  the 
lake  shore  in  Orwell  just  north  of  the  Benson  line.  A,  Black  River ; 
B,  Trenton ;  C,  Trenton-"Utica"  ;  D,  friable  shales  probably  conform- 
able with  C;  E,  "Potsdam"  and  "Beekmantown"  now  lying  by  thrust 
on  A,  B,  C,  and  formerly  also  on  D.  A  normal  fault  has  dropped  the 
rocks  at  the  left,  including  the  thrust  plane.  On  the  upthrow  side  B  has 
been  eroded  and  also  part  of  D.      1-2,  thrust  plane. 


Southeast  of  the  old  farm  mentioned  above  is  a  very  bold 
precipitous  scarp  in  the  dolomite.  In  the  face  of  this  clifif  the 
rocks  appear  very  massive  and  exhibit  little  appearance  of 
bedding.  The  scarp  loses  prominence  southward  owing  to  the 
drift  piled  against  it;  but  it  was  followed  through  the  woods 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  155 

above  the  camp  of  Oscar  Neemes  to  an  apparent  fault  that  will 
presently  be  described. 

Along  the  shore  one-half  mile  south  of  "Blue  Ledge"  and 
only  a  few  rods  north  of  Neemes'  camp,  very  thick,  bluish-black 
limestone  beds  appear  in  the  bank  and  dip  into  the  lake.  The 
water  line  intersects  diagonally  the  strike  of  these  thick  limestone 
beds  and  as  one  walks  along  the  shore  one  passes  from  syncline 
to  anticline,  rather  closely  spaced  and  regular  in  their  succession 
and  probably  as  strongly  compressed  as  these  heavy  beds  would 
allow.  South  of  Neemes'  camp  the  beach  is  covered  with  many 
boulders  in  which  Bellerophon,  Trinucleus,  Plectambonites  and 
other  fossils  are  common.  Above  the  bank  apparent  Trenton 
beds  outcrop  and  many  loose  boulders  are  filled  with  Trenton 
fossils. 

South  of  an  east-west  line  passing  approximately  through 
Neemes'  camp  what  are  apparently  Middle  Ordovician  strata  have 
a  topographic  level  about  the  same  as  massive  Beekmantown 
north  of  that  line.  South  of  this  hypothetical  line,  back  in  the 
woods  about  one-fourth  of  a  mile  southeast  of  the  old  Walker 
place,  a  quartzitic  sandstone  forms  a  low  cliff.  The  scarp  is 
farther  east  of  the  shore  than  that  of  the  massive  Beekmantown 
just  north  of  Neemes'  camp.  There  may  be  an  east-west  fault 
with  an  offset,  in  the  vicinity  of  the  camp,  and  with  differential 
lateral  displacement ;  or,  as  the  topography  affords  reason  for 
thinking,  while  there  may  be  a  fault  the  quartzite  scarp  south  of 
it  may  owe  its  present  more  easterly  recessive  position  to  erosion 
of  rocks  left  at  a  relatively  higher  topographic  level  after  normal 
faulting. 

The  thick-bedded,  bluish-black  limestones  just  described  are 
regarded  as  probably  Black  River,  both  from  their  lithology  and 
stratigraphic  relation  to  apparent  Trenton  rocks.  It  is  not  wholly 
certain  whether  they  and  the  Trenton  are  part  of  the  overriding 
mass,  or  are  beneath  it  like  the  "Utica"  farther  north.  In  figure 
11  they  are  represented  as  beneath.  They  may  have  participated 
in  a  thrust,  or  a  reverse  fault,  and  also  be  overthrust  by  older 
rocks. 

The  evidence  afforded  by  the  relations  along  the  Champlain 
shore  in  Orwell  favors  the  views : 

1.  That  the  Middle  Ordovician  strata  (Trenton-Utica)  are 
overlain  by  early  Ordovician  (Beekmantown)  or  possibly  even 
older  ("Potsdam")  rocks; 

2.  That,  as  indicated  by  the  absence  of  any  but  relatively 
gentle  flexures,  which  indeed  were  probably  due  to  much  later 
deformation  than  that  which  produced  its  present  superposition, 
the  older  rock  was  thrust  bodily  over  the  younger  strata  and  now 
lies  unconf  ormably  upon  the  latter  along  a  thrust  plane ; 

3.  That  a  later  crustal  disturbance  deformed  the  whole 
series,  including  the  thrust  plane,  and  caused  irregular,  gentle 


156  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

flexures  in  the  thick  overthrust  mass,  which  as  now  eroded  dis- 
plays the  basal  Ordovician  and  perhaps  Upper  Cambrian  lying 
on  the  younger  rocks ; 

4.  That,  at  the  time  of  the  disturbance  just  mentioned,  or 
later,  there  occurred  some  faulting  with  various  degrees  of  dis- 
placement, involving  the  rocks  both  above  and  below  the  thrust 
plane ; 

5.  That  the  major  thrust  plane  which  parted  the  thick  mass 
of  strata  composing  the  Lower  Ordovician  of  the  region  did  not 
shear  always  at  the  same  stratigraphic  level,  but  cut  through  it 
so  that  the  rupture  was  now  through  the  Beekmantown  and  now 
through  the  "Potsdam." 

These  conclusions  seemed  reasonably  clearly  established 
before  the  relations  in  Orwell  east  of  the  shore  were  examined. 

Relations  west,  northzvest  and  southwest  of  Onvell  village. 
East  of  the  lake  in  the  bottoms  of  ravines  tributary  to  East  Creek 
are  many  small  exposures  of  friable  slates  and  shales  with  easterly 
dip.  Still  farther  east  in  the  banks  and  bed  of  the  North  Branch 
of  East  Creek  in  various  parts  of  its  course  the  slates  again  out- 
crop and  show  frequent  bands  of  interbedded  black  limestone. 
These  slates  were  traced  eastward  along  East  Creek  and  the 
North  Branch  to  the  western  margin  of  the  limestone  formations 
west  of  Orwell  village. 

•  One  and  a  half  miles  west  of  the  village,  East  Creek  tumbles 
over  the  edge  of  limestone  and  cataracts  across  upturned  slates. 
This  place  is  the  site  of  an  old  grist  mill,  formerly  known  as 
"Chittenden's  Mill." 

At  the  summit  of  the  falls  the  rock  is  a  dark  blue  or  black 
limestone  which  breaks  into  splintery  pieces.  The  beds  strike 
N.  about  38°  E.  and  dip  southeasterly.  This  limestone  carries 
number  of  Prasopora  lycoperdon  on  the  eroded  surface  and 
when  broken  gave  Trinucleus  and  linguloid  shells.  About  half 
way  down  the  cataract  slopes  in  the  brook  bed  a  reading  in  the 
slates  and  interbedded  limestones  gave  N.  77°  E.  There  has 
clearly  been  disturbance. 

About  one  mile  northwest  of  HufT's  Crossing,  a  few  rods 
east  of  the  railway  track  is  a  high  scarp  in  massive,  siliceous 
dolomite  (see  plate  XXV).  At  the  base  are  beds  like  those  at 
the  base  of  Mt.  Independence  and  probably  representing  the 
"Potsdam"  of  Brainerd  and  Seely;  but  the  slates  on  which  this 
rock  presumably  rests,  by  analogy  with  conditions  farther  south 
on  the  lake  shore,  were  not  seen.  Along  the  road  east  of  the 
scarp  are  beds  like  those  overlying  the  "Potsdam"  at  Mt.  Inde- 
pendence. 

In  the  bed  and  banks  of  the  North  Branch  around  Huff's 
Crossing  are  exposed  higher  beds  of  the  Beekmantown  formation, 
and  three-fourths  of  a  mile  farther  south  some  of  these  latter 
beds  are  exposed  in  numerous  outcrops  in  the  fields  near  the  road. 


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REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  1 

These  exposures  have  been  described  by  Brainerd  and  Seely. 
The  blue  limestone  of  their  division  D  appears  on  the  axis  of 
the  anticline  carrying  Ophileta  complanata,  Maclureas  and  other 
fossils.  This  member  is  succeeded  on  each  Hmb  by  the  other 
members  of  this  division,  although  those  on  the  east  limb  are 
most  satisfactory  for  study.  In  the  stream  channels  near  Huff's 
Crossing  divisions  D  and  E  appear  and  in  addition  the  top  of 
division  C. 

West  of  the  highway  bridge  at  Huff's  Crossing  the  Beekman- 
town  beds,  which  directly  beneath  the  bridge  lie  in  a  flat  position, 
as  displayed  in  the  south  bank  of  the  stream  through  a  distance 
of  about  300  yards  show  gentle  undulations  with  apparently 
slight  southerly  pitch.  Then  appears  an  abrupt  change  from  a 
moderate  dip  to  one  about  65°  W.  along  a  strike  of  about  N.  25° 
E.  About  60  or  70  feet  of  interstratified  limestone  and  siliceous 
beds  are  exposed  across  their  strike  in  the  bed  of  the  stream. 
About  100  paces  west  of  these  rocks  are  similar  ones  which  show 
a  somewhat  puddled  arrangement  which  is  attributed  to  the  dis- 
turbance which  these  rocks  have  suffered.  Two  hundred  paces 
downstream,  after  an  interval  of  clay,  appear  the  blackish  slates 
with  limestone  bands  like  those  seen  near  the  grist  mill  falls, 
westward  at  intervals  along  East  Creek,  and  at  the  lake  shore. 

A  mile  and  half  south  of  these  exposures,  north  of  the  road 
which  runs  westerly  north  of  the  grist  mill  falls,  along  the  west 
edge  of  the  woods  and  west  of  Beekmantown  beds,  were  found 
numerous,  well-preserved  surface  scrolls  of  Maclurea  magna  at 
numerous  places  and  other  outcrops  of  striped,  bluish  limestone 
like  the  Chazy  as  seen  at  other  locaHties.  West  of  this  stratum 
are  limestones  carrying  hosts  of  surface  markings  of  fossils  and 
which  are  regarded  as  probably  representing  the  Trenton.  These 
various  rocks  seem  more  metamorphosed  than  the  Trenton  rocks 
above  and  the  slates  below  the  dam  at  the  grist  mill  and  in  some 
cases,  at  least,  have  a  highly-inclined  westerly  dip. 


Figure  12.  A  section  generalized  to  show  interpretation  of  structure  in  the 
overthrust  Lower  Ordovician  limestones  (here  largely  "Beekmantown") 
west  of  Orwell  village.  The  massive  rocks  were  ruptured  by  reverse 
faults  which  were  subsequently  truncated  by  a  thrust,  1-2.  The  rocks 
were  carried  westward  over  folded  limestones  and  slates  belonging  to 
the  Trenton-"Utica"  formations  of  the  present  lake  region.  1-2,  thrust 
plane. 


158  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

From  the  general  local  deformation  shown  along  the  western 
edge  of  this  eroded  anticline  south  of  Huff's  Crossing  it  would 
appear  that  there  was  a  rupture  following  compression  of  the 
rocks  composing  it  and  that  along  the  plane  of  rupture  there  was 
differential  movement  and  friction  which  occasioned  more  flexing 
than  these  massive  rocks  usually  underwent  and  which  brought 
about  some  overturning.  So  far  as  observed  in  the  massive 
strata  found  overlying  the  slate  formation  in  this  immediate 
region,  strong  flexure  does  not  appear  to  have  been  their  mode 
of  deformation,  from  which  fact  the  inference  is  drawn  that  the 
structure  just  described  was  due  to  friction  and  of  the  nature  of 
a  drag  rather  than  one  that  preceded  and  initiated  the  break. 

At  the  grist  mill  falls  the  eastern  and  western  walls  of  the 
gorge  are  apparently  composed  of  massive  beds  lying  rather 
flat,  and  like  those  which  extend  with  some  interruption  west- 
ward and  southwestward  toward  the  lake,  and  which  form  a 
noticeable  scarp  along  the  road  to  Montcalm  Landing.  From 
general  field  relations  and  lithology  most  of  these  rocks  are  cor- 
related with  the  Beekmantown,  although  their  exact  position 
therein  could  not  be  made  out  with  certainty.  From  the  dis- 
cordance in  structure  in  the  walls  of  the  gorge  it  seems  most 
probable  that  the  massive  so-called  Beekmantown  rests  uncon- 
formably  upon  the  slate  formation  and  that  it  also  once  overlay 
the  fossiliferous  rocks  at  the  summit  of  the  falls.  The  condi- 
tions did  not  permit  a  good  photograph.  The  massive  strata 
seem  not  to  be  so  severely  deformed  as  the  similar  rocks  lying 
north  of  them  and  it  is  regarded  as  probable  that  an  east- west 
break  lies  between.  The  interpretation  of  probable  general 
structure  is  shown  in  figure  12,  which  does  not  attempt  to  show 
the  probable  normal  faulting  just  mentioned. 

The  massive  magnesian  rocks  that  extend  westerly  from  the 
grist  mill,  about  a  half  mile  west  of  the  dam  are  interrupted 
along  the  road  and  in  the  fields  by  slates  which  in  one  outcrop 
showed  westerly  dip.  The  field  relations  indicate  that  these  slates 
are  surrounded  by  the  dolomite  and  have  been  exposed  by  the 
erosion  of  the  latter.  Westward  the  road  to  Montcalm  Land- 
ing descends  over  a  scarp  in  the  dolomite  to  the  Champlain  clays 
that  extend  to  the  lake  shore.  This  scarp  is  on  a  meridian  a 
mile  west  of  that  on  which  is  located  the  axis  of  the  anticline 
south  of  Huff's  Crossing.  The  rocks  composing  this  scarp  are 
apparently  in  somewhat  interrupted  surface  continuity  with  other 
magnesian  rocks  which  form  the  slopes  and  summit  of  a  hill 
about  one  mile  south  of  it,  the  upper  beds  of  which  are  yellowish 
or  somewhat  chamois-colored  rocks  and  which  grade  downward 
into  other  rocks  which  could  not  be  correlated  with  certainty  on 
account  of  drift  and  few  exposures,  but  which  towards  the  base 
contain  cherty  dolomites  like  those  of  Mt.  Independence, 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  159 

Additional  considerations  concerning  the  general  structure 
of  the  region.  From  the  outcrops  and  relations  just  described 
for  the  areas  inland  from  the  lake  and  west  of  Orwell  village 
it  seems  that  further  support  and  suggestions  may  be  drawn  as 
to  the  interpretations  to  be  put  upon  the  structure  of  the  region 
along  the  lake. 

1.  The  structural  relations  at  the  grist  mill  gorge,  taken 
with  the  general  procumbent  position  of  the  massive  strata ;  the 
difference  apparent  in  the  metamorphism  of  the  rocks  which  are 
now  in  contiguity;  and  the  patch  of  slates  lying  west  of  the 
grist  mill  which  is  seemingly  surrounded  with  massive  magnesian 
limestone  beds  and  has  therefore  the  character  of  an  erosion  out- 
lier, give  further  support  to  the  idea  that  the  Beekmantown  strata, 
and  possibly  older  rocks,  now  rest  on  the  slate  formation  and 
probably  some  Trenton  rocks  included  or  in  addition,  along  a 
thrust  plane. 

2.  That  the  massive  overriding  strata,  either  during  or 
prior  to  translation,  were  broken  along  a  reverse  strike  fault  and 
that  a  slight  buckle  occurred  east  of  the  fracture  with  some  fold- 
ing down  of  the  edges  of  the  beds  along  the  western  margin  of 
the  block  that  was  pushed  against  the  adjacent  beds  on  the  west; 
and  that  possibly  some  Chazy  and  possibly  still  younger  beds 
were  involved  in  the  frictional  drag  along  this  reverse  fault 
plane. 

3.  That  there  may  have  been  some  warping  or  faulting 
later  that  dropped  the  strata  between  the  gorge  and  the  scarp 

.  north  of  Huff's  Crossing  and  left  the  intervening  beds  at  a  lower 
level  than  those  on  each  side  of  these  faults,  or  in  the  trough  of 
the  warp,  and  thus  preserved  beds  higher  than  the  Beekmantown 
at  the  present  erosion  surface. 

4.  That  the  various  scarps  in  the  dolomite  formation  stand 
primarily  for  the  major  thrust  relation  which  this  formation  bears 
to  the  slates ;  and  that  some  structural  features  secondary  to  the 
thrust  favored  the  erosion  of  the  Beekmantown  between  the  de- 
tached masses  of  these  rocks  near  the  lake  shore  and  their  sinuous 
inland  margin  which  is  often  marked  by  scarps. 

5.  That  the  massive  character  of  the  overthrust  rocks  pre- 
vented much  heaping  up  by  reverse  faulting  under  the  com- 
pression. 

6.  That  the  plane  of  major  thrust  is  now  and  probably  was 
originally  one  of  low  angle  to  the  horizontal. 

Areas  north,  east  and  south  of  Orwell  village.  The  Beek- 
mantown rocks  forming  the  anticline  south  of  Huff's  Crossing 
were  traced  eastward  by  scattered  outcrops  across  their  strike  to 
the  old  ?tage  road  to  Shoreham  village  and  in  places  fossils  were 
noted  on  the  weathered  surfaces.  These  fossils  appeared  as 
Maclurea-  or  Ophileta-like  scrolls  with  others  that  resembled 
cephalopods  in  the  shape  of  the  outlines  and  in  the  presence  of 


160  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

septa.  East  of  the  stage  road  markings  are  less  numerous  and 
distinct  and  outcrops  fewer  on  account  of  drift.  On  the  basis 
of  fossils  and  structure  and  also  certain  other  exposures  that 
will  be  described  presently  lying  to  the  eastward,  the  beds  over 
an  east-west  distance  of  a  mile  east  of  the  road  from  Orwell 
village  to  Larrabee's  Point  are  regarded  as  Beekmantown  in  age. 

East  of  the  road  from  Orwell  village  to  Orwell  depot,  lime- 
stone outcrops  are  numerous  and  form  a  band  a  half  mile  wide 
resting  against  the  western  slope  of  Deignault  Hill.  Maclurea 
magna  was  found  by  the  writer  near  the  western  edge  of  this 
band.  East  of  the  beds  carrying  this  fossil  the  limestone  shows 
abundant  fossil  markings  on  the  weathered  surfaces,  but  the 
rock  is  so  altered  that  nothing  distinct  could  be  seen  on  fresh 
surfaces.  At  many  places  sections  of  shells  both  in  the  plane 
of  the  spiral  and  at  right  angles  to  the  axis,  strongly  resemble 
Pleurotomaria  and  Murchisonia.  A  number  of  the  more  robust 
Pleurotomaria-like  forms  were  abraded  to  the  plane  of  the 
columella  and  left  little  doubt  of  their  generic  affinity.  Spiral 
coils  at  right  angles  to  the  axis  of  the  whorls  were  very  common. 
Crinoid  sterrts  were  frequent.  From  these  characters  the  rock 
is  regarded  as  probably  of  Trenton  age.  It  bears  closest  litho- 
logical  resemblance  to  other  rock  that  will  be  described  beyond  in 
which  still  more  characteristic  fossils  were  found  with  those  just 
described. 

These  limestone  beds  have  a  general  north-northeast  strike 
and  seem  to  occur  in  somewhat  undulating  open  folds.  There  is 
a  prevailing  easterly  dip  due  to  shearing  deformation  which  has 
greatly  obscured  the  stratification  dip.  At  some  places  an  ap- 
parent flattish  position  and  at  others  a  westerly  dip  of  the  bedding 
were  observed. 

The  limestones  just  described  are  succeeded  eastward  at  the 
surface  by  phyllites  and  schists  on  which  they  apparently  rest, 
although  no  contact  was  seen.  Along  the  road  from  Orwell 
village  on  the  west  slope  of  Deignault  Hill  outcrops  of  the  phyl- 
lites intervene  between  others  of  limestone,  but  a  short  way 
beyond  the  eastern  margin  of  the  limestone  is  reached  and  may 
be  followed  in  a  north-northeasterly  direction  just  west  of  the 
road  running  northerly  at  the  top  of  the  hill.  The  instance  cited 
above  was  the  only  one  noted  northeast  of  Orwell  village  where 
the  limestone  has  been  eroded  so  as  to  expose  a  patch  of  the 
underlying  phyllite.  East  of  the  limestone  margin  all  is  phyllite 
for  a  mile  or  more  to  the  valley  of  the  Lemon  Fair  River. 

The  limestones  just  described  vary  in  degree  of  metamor- 
phism  along  the  strike  and  present  certain  interesting  characters 
in  their  outcrops  in  proximity  to  the  phyllite.  Just  east  of  the 
main  village  of  Orwell,  north  of  the  road  to  Sudbury,  the  lime- 
stones are  strongly  sheared  and  are  almost  slates.  Many  surface 
exposures  are  "marbly"  in  appearance.     Near  the  phyllite  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  161 

limestone  is  frequently  seamed  with  many  veinlets  of  calcite,  a 
feature  which  was  observed  at  mariy  places  in  this  general  region 
where  the  limestone  and  phyllite  are  close  together  in  surface 
outcrops,  or  where  there  is  good  reason  to  think  that  the  phyllite 
is  only  a  short  distance  beneath  the  limestone. 

The  limestones  northeast  of  Orwell  village  continue  along 
the  strike  south  and  southwest  of  the  village  with  prevailing 
easterly  dip  which  is  for  the  most  part  a  shearing  deformation 
structure  purely.  One-fourth  of  a  mile  south  of  the  village 
distinct  easterly  stratification  dip  is  apparent  and  the  rock  carries 
sections  of  Mure  his  onia-like  forms.  In  general  the  rock  south  of 
the  village  as  far  as  the  old  stage  road  resembles  the  Trenton  at 
the  north. 

West  of  the  road  the  limestone  seems  to  be  more  metamor- 
phosed generally,  is  strongly  sheared  and  seamed  with  calcite  in 
many  places,  and  often  takes  on  a  "marbly"  appearance.  At  one 
place  a  sort  of  flow-cleavage  structure  seemed  to  have  been 
developed  nearly  parallel  to  the  bedding  and  both  apparently 
were  subsequently  folded.  The  fold  is  now  cut  by  two  sets  of 
fracture  planes. 

South  of  Orwell  village  the  limestones  give  place  easterly 
at  the  surface  to  phyllites,  schists  and  slates  which  are  the  south- 
ward continuation  of  those  in  Deignault  Hill.  These  terrigenous 
rocks  form  the  high  hills  in  the  southern-central  part  of  the 
township  around  Sunset  Lake  and  its  neighboring  ponds,  and 
extend  into  Benson  township  at  the  south.  Two  miles  south- 
southwest  of  Orwell  village,  just  east  of  the  Benson-Orwell 
road,  begins  a  series  of  scarps,  which  increase  in  altitude  south- 
ward and  which  mark  a  normal  fault  displacement.  At  numer- 
ous places  in  the  hills  east  of  these  scarps  are  cliffs  that  are  in- 
terpreted as  fault  scarps  and  some  of  the  ponds  rest  in  what  are 
apparently  primarily  faulted  basins. 

About  a  mile  north  of  the  Benson  line  on  the  downthrow 
side  of  the  great  fault  the  limestones  along  the  valley  of  East 
Creek  give  place  at  the  surface  to  phyllites  which  extend  westerly 
as  shown  on  the  map.  Over  the  phyllite  lying  west  of  the  fault 
and  in  the  high  hills  east  of  it  no  limestone  was  discovered. 

The  wider  surface  exposure  of  the  phyllite  formation  at  the 
south  in  Orwell  township  is  to  be  associated  with  its  present 
higher  altitude  and  conditions  which  favored  the  erosion  of 
limestone  that  once  overlay  it ;  for  the  field  relations  east  and 
south  of  this  spur  of  high  land  show  that  limestone  of  similar 
age  and  character  to  that  which  in  Orwell  rests  against  or  on  the 
schist  at  the  west  lies  on  entirely  similar  phyllite  east  of  the  spur 
and  indicate  the  former  extension  of  the  limestone  over  the 
phyllite  now  forming  the  spur. 

Eastern  Orwell  township.  A  strip  of  country  about  a  mile 
and  a  half  wide  in  the  eastern  part  of  Orwell  township  presents 


162  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

many  significant  features.  The  northern  part  of  this  strip  is  now- 
very  largely  buried  by  Champlain  clays,  but  the  southern  part  is 
hilly  and  affords  many  interesting  outcrops  \v1iich  serve  to  bring 
out  the  general  relations  among  the  rock  formations. 

South  of  the  Orwell-Sudbury  road  are  two  valleys  separated 
by  a  low  range  of  hills.  Along  the  western  valley  extends  the 
road  from  Abell  corner  to  Bangall  and  Hortonville,  The  other 
valley  is  occupied  by  the  head  stream  of  Lemon  Fair  River  and 
along  its  western  margin  is  another  road  going  also  to  Horton- 
ville. Along  these  valleys  and  over  the  low  range  intervening 
between  them  the  surface  rock  is  largely  limestone,  which  can  be 
seen  to  have  been  much  disturbed  by  folding  and  faulting  and 
to  have  been  severely  sheared  in  most  places.  The  prevailing 
rock  is  of  a  faded  blue  or  gray  color  on  weathered  surfaces  and 
dark  blue  or  bluish-gray  on  fresh  surfaces.  So  far  as  observed 
it  does  not  often  take  on  a  "marbly"  aspect  south  of  the  Orwell- 
Sudbury  road.  Fossils  were  found  at  many  places  in  this  lime- 
stone on  the  hills  and  in  both  valleys  mentioned,  chiefly  on  the 
weathered  surface.  They  all  have  a  similar  aspect  and  consist 
of  crinoid  stems,  scrolls  representing  shells  of  gastropods  like 
those  found  northeast  of  Orwell  village,  sections  in  the  planes 
of  the  axes  of  spirals  resembling  Pleurotomaria  and  Murchisonia, 
Plectambonites,  Orthis,  a  doubtful  streptelasmoid  form,  a  small 
and  a  medium-sized  Orthoceras,  bryozoans  like  Stictopora  and, 
on  fresh  surfaces,  many  specimens  of  Triniicleus.  The  most 
prolific  localities  were  found  on  the  adjoining  farms  of  George 
W.  Felton  and  Horton  Farnum  along  a  side  hill  just  west  of  the 
eastern  road  mentioned  above.  Southeast  and  east  of  Farnum's, 
similar  rock  extends  east  of  the  road  across  the  Lemon  Fair 
valley  and  similar  fossils  were  found  at  several  places  nearly  to 
the  Hyde  Manor  road. 

For  the  most  part  the  limestone  just  described,  so  far  as 
the  shearing  structure  permits  observation,  consists  of  beds  of 
moderate  thickness  and  in  this  and  in  general  lithologic  features 
as  well,  resembles  the  Trenton  northeast  of  Orwell  village  and, 
in  fact,  also  that  along  the  lake  near  Neemes'  camp.  But  it 
should  be  noted  that  metamorphism  is  clearly  more  pronounced 
in  the  areas  east  of  the  lake  shore. 

In  Horton  Farnum's  pasture  were  seen  some  massive  beds 
of  limestone  which  from  the  field  relations  seemed  to  be  inferior 
to  the  fossiliferous  beds  lying  north  and  south  of  them.  There 
was  nothing  seen  to  indicate  whether  the  massive  beds  are  of 
the  same  age  as  those  surrounding  them  or  older.  See  plate 
XXVL 

At  various  places  along  both  valleys  mentioned,  on  each 
side  of  both  roads  and  within  the  low  range  of  hills  intervening, 
phyllite  or  quartzite  emerges  at  the  present  surface  from  be- 
neath the  broken  and   eroded   limestones.     The   map  does  not 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  163 

attempt  to  show  fully  the  fragmentary  nature  of  these  outcrops 
of  terrigenous  rocks.  They  appear  sometimes  as  patches  sur- 
rounded by  limestone,  sometimes  as  scarps  along  the  strike  on 
hill  summits,  sometimes  but  more  rarely  in  sections  across  the 
strike  in  gulleys  of  erosion,  and  again  as  narrow  bands,  as  though 
in  faulted  or  infolded  with  the  limestone.  These  terrigenous  rocks 
are  entirely  similar  to  those  of  the  Orwell  hills  and  to  those  of 
the  Sudbury  hills  lying  to  the  eastward,  and  it  was  not  possible 
to  draw  any  distinctions  among  them  on  the  basis  of  difference 
in  age,  or  from  their  relations  to  the  associated  limestones. 

North  of  the  Orwell-Sudbury  road  the  course  of  the  Lemon 
Fair  has  been  constrained  and  controlled  in  the  process  of  the 
river's  down-cutting  by  a  few  ledges  which  by  the  river's  work 
and  that  of  general  erosion  have  been  opened  to  view.  Some  of 
these  ledges  are  of  much  interest. 

Outcropping  in  the  west  bank  of  the  Fair  in  the  fields  about 
one  and  a  half  miles  north-northeast  of  Abell  corner  and  ex- 
posed on  the  dip  surface  is  the  light  blue  limestone  seen  south  of 
the  Orwell-Sudbury  road.  In  the  east  bank  of  the  stream  the 
beds  are  exposed  along  their  edges  and  much  of  the  rock  is 
seen  to  be  a  strongly-sheared  limestone  having  the  character  of 
a  calcareous  slate.  Practically  on  the  strike  of  these  beds,  a  few 
rods  north  in  the  same  bank  and  in  a  somewhat  higher  scarp, 
this  sheared  limestone  takes  on  a  "marbly"  aspect  and  is  infolded 
or  infaulted  with  patches  of  chamois-colored,  dolomitic  rock. 
Near  the  base  of  the  section  light-colored,  siliceous  phyllites  like 
those  so  frequent  in  the  Orwell  and  Sudbury  hills,  and  outcrop- 
ping through  the  limestones  lying  between,  emerge  from  beneath 
the  marbly  rocks  and  at  one  place  a  large  solution  hole  has  ex- 
posed the  phyllite  underlying  the  limestone.  Northerly  the 
sheared  rock  becomes  still  more  "marbly"  and  lies  above  strongly- 
sheared,  slaty  limestone. 

In  this  general  vicinity  the  limestone  or  "marble"  is  filled 
with  solution  holes  and  channels  along  joints  which  give  an  im- 
pression that  the  limestone  lies  in  disturbed  relation  to  some 
stratum  beneath. 

The  sheared  "marble"  extends  through  the  fields  eastward 
from  the  Fair  for  several  rods  and  gives  place  at  the  surface  to 
a  sheared,  light-blue  rock  like  that  noted  on  the  west  of  the  Fair. 
It  is  infolded  with  gray  dolomite  mentioned  above. 

The  sheared  blue  rock  and  "marble"  are  thus  seen  ap- 
parently to  pass  into  one  another  both  along  and  across  the 
strike  in  these  exposures  and  apparently  both  have  essentially  the 
same  relations  to  the  gray  or  chamois-colored  beds.  The  gray 
rock  is  also  found  south  of  the  Orwell-Sudbury  road,  but  its 
relations  there  are  not  impressive.  Conditions  similar  to  those 
just  described  for  the  rocks  in  the  banks  of  the  Fair  and  adjacent 
fields,  north  of  the  Sudbury  road,  prevail  in  the  fields  east  and 


164  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

south  and  need  not  be  cited  in  detail.  It  may  be  noted  that 
entirely  similar  types  and  relations  extend  through  detached  ex- 
posures southeastward  to  the  west  slope  of  Sudbury  Hill  below 
the  stage  road. 

The  field  relations  of  the  blue  limestone  or  "marble"  to  the 
gray  dolomite  suggests  that  the  dolomite  is  not  interbedded  with 
the  other,  but  that  it  is  usually  above  it  and  distinct  from  it.  The 
examination  of  some  of  the  exposures  in  which  the  two  are  in- 
folded, or  infaulted,  might  give  the  impression  that  the  two  are 
interbedded  members  of  the  same  formation. 

For  some  reason  the  rocks  north  of  the  Orwell-Sudbury  road 
have  been  more  severely  altered  and  fossils  in  them  now  seem 
to  be  lacking. 

RUTLAND   COUNTY. 

Benson  Township. 

(Whitehall  topographic  sheet.) 

Topography.  Hubbardton  River  and  its  head  streams  have 
cut  their  valleys  below  the  level  of  300  feet  among  the  hills  in  the 
eastern  part  of  the  town,  and  a  strip  along  the  lake  shore  in  the 
northwestern  part  a  mile  wide  and  a  mile  and  a  half  long  marks 
a  small  extension  of  the  Champlain  lowland  into  this  area.  Else- 
where Benson  topography  is  typical  of  the  foothill  country  west 
of  the  Taconic  range. 

Description  of  a  section  from  Lake  Champlain  through 
Benson  village  to  Bangall,  near  Hortonville.  Extending  from 
Benson  Landing  for  a  distance  of  one  and  a  half  miles  eastward 
along  the  road  from  the  landing  to  Benson  village  the  section 
gives  siliceous  and  magnesian  limestones  of  Brainerd  and  Seely's 
Beekmantown  formation.  The  beds  form  a  gentle  arch  and  near 
the  lake  dip  at  a  low  angle  to  the  west. 

At  Benson  Landing  the  Beekmantown  rocks  as  exposed  do 
not  reach  the  lake  shore,  but  a  mile  north  at  Stony  Point  they 
dip  into  the  lake.  A  few  rods  east  of  Benson  Landing  are  ex- 
posed in  a  low  west-facing  clifif  in  a  ravine  south  of  the  road 
about  15  feet  of  dark,  bluish-gray,  siliceous  limestone  or  dolomite, 
weathering  light  gray,  in  beds  about  two  feet  thick  which  dip 
gently  to  the  west.  About  20  rods  to  the  east  of  this  outcrop  is  a 
somewhat  higher  cliff  in  the  ravine  showing  from  the  base  about 
two-thirds  the  way  up,  massive  beds  of  somewhat  pitted,  magne- 
sian limestone  which  on  fresh  surfaces  is  mottled  light  and  dark 
gray.  Above  these  beds  are  a  few  feet  of  limestone  showing  many 
ridges  parallel  with  the  bedding.  The  dip  is  gently  westward. 
Above  these  rocks,  in  and  beside  the  road  and  perhaps  20  feet 
higher  stratigraphically,  near  the  junction  with  the  Stony  Point 
road  and  in  the  yard  of  the  William  White  place,  are  exposed 
with  westerly  dip  bluish-gray  limestones  frequently  covered  with 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  165 

thick,  reticulated,  gray  or  reddish  brown  patches,  which  often 
show  as  shallow,  ringed  craterlets  in  relief  which  give  the  weath- 
ered surface  a  coarsely-pitted  appearance.  Among  these  pits  and 
patches  and  also  on  the  smoothly-weathered  rock  are  scores  of 
finely-coiled  whorls  of  Ophiletas  and  some  Maclureas.  These 
fossiliferous  beds  are  interstratified  with  layers  of  sandstone. 
Eastward  about  200  yards  along  the  road,  dark,  bluish-gray  rock 
somewhat  like  that  noted  in  the  first  clifif  outcrops  beside  the 
road  and  a  half  mile  east  similar  rock  lies  flat.  Away  from  the 
lake  the  outcrops  are  few  and  mere  patches  in  the  drift.  The 
precise  sequence  was  therefore  hard  to  determine;  but  it  seemed 
clear  that  probably  the  fossiliferous  rock  represents  the  lowest 
subdivision  of  Brainerd  and  Seely's  Division  D,  carrying  Ophileta 
complanata,  Vanuxem. 

The  magnesian  limestones  lying  beneath  the  fossiliferous 
beds  presumably  represent  Division  C.  All  the  rocks  appear 
conformable,  but  the  conditions  do  not  permit  minute  comparison 
with  similar  rocks  in  the  sections  of  Shoreham  and  Orwell. 

Eastward  along  the  road  past  the  school  house  at  William- 
son corner  and  down  the  slope  to  a  brook  are  occasional  ex- 
posures which  are  not  readily  identified  or  correlated  in  their 
restricted  outcrops. 

South  of  the  brook  and  the  road  are  mud-colored  slates 
which  a  few  hundred  feet  eastward  up  the  brook  give  place  to 
bluish  or  dove-colored  limestones  intermingled  with  chamois- 
colored  dolomite.  The  dove-colored  rock  carries  dirty,  yellowish 
patches  and  stripes  often  soiled  to  black  and  on  its  weathered 
surface  at  places  afforded  many  small  fragments  of  indetermin- 
able fossils  and  two  recognizable  specimens  of  Maclurea  magna. 
A  reading  gave  the  strike  as  N.  32°  E.  and  the  dip  as  25°  easterly. 

East  of  these  rocks  a  short  distance,  on  the  north  side  of  the 
road,  are  limestones  resembling  the  Trenton  beds  near  Horton- 
ville,  which  will  be  described  presently.  No  fossils  were  found. 
East  of  these  exposures,  along  the  road,  the  rocks  are  slates, 
some  of  which  are  mud-colored,  friable  rocks  like  those  men- 
tioned above  as  occuring  at  the  present  surface  farther  west 
between  probable  Beekmantown  and  Chazy  outcrops  and  which 
have  what  appears  to  be  a  distinguishable  difference  from  most 
of  the  slates  of  the  Benson  hills.  They  have  in  fact  a  resemblance 
to  certain  slaty  or  shaly  rocks  which  were  noted  farther  north  in 
Orwell,  but  which  have  not  thus  far  been  described  in  a  special 
way.  In  some  of  the  ravines  tributary  to  East  Creek  in  Orwell 
the  friable  shales  did  not  appear  precisely  like  the  blacker  so- 
called  "Utica"  and  led  to  the  suspicion  that  there  is  a  series  of 
beds  in  the  formation  that  usually  goes  under  the  comprehensive 
name  of  "Utica"  which  is  marked  by  less  carbonaceous  matter 
and  whose  members  are  of  prevailingly  different  color.  This 
idea  seemed  to  receive  some  confirmation  when  mud-colored  slates 


m.  OF  Mfcss.  mm  imm 


166  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

were  found  west  of  the  grist  mill  on  East  Creek  along  the  road 
to  Montcalm  Landing  and  therefore  lying  west  of  the  black, 
compact  Trenton  limestone  and  associated  black  slates  at  the 
dam  and  in  the  gorge  of  the  creek  and  again  when  similar  slates 
were  found  on  the  meridian  of  those  west  of  the  grist  mill  two 
miles  to  the  south  along  the  road  to  the  lake  that  passes  through 
Frank  Charleton's  farm,  and  also  a  mile  south  of  here  on  the 
hill  east  of  the  Nefong  farm  (old  Walker  place)  and  east  of  the 
road  from  the  Nefong  farm  to  Benson  Landing. 

The  mud-colored  slates  along  the  road  from  Benson  Landing 
to  Benson  village  lie  on  the  general  meridian  of  the  various  ex- 
posures, of  similar  slates  just  mentioned  as  occurring  in  Orwell 
and  are  now  regarded  by  the  writer  as  the  same.  Along  the 
Benson  road  they  give  place  at  the  surface  to  black  slates  which 
have  been  called  "Benson  Black  Slates."  An  actual  transition 
was  not  noted.  Outcrops  of  the  mud-colored,  friable  slates, 
however,  occur  close  to  those  of  the  black  slates ;  but  after  the 
latter  begin,  going  eastward,  there  do  not  appear  to  be  any  more 
outcrops  of  the  lighter-colored  and  more  friable  slates.  A  similar 
relation  obtains  at  the  north ;  in  northern  Benson  township,  on 
the  downthrow  side  of  the  great  scarp  along  the  Benson-Orwell 
road,  a  blackish  slate  is  present  and  westward  across  East  Creek 
the  other  slates  appear. 

The  black  slates  continue  eastward  through  Benson  village 
and  east  of  the  village  are  succeeded  by  outcrops  of  lighter- 
colored,  siliceous  phyllites  like  those  that  are  intermingled  with 
the  black  phyllites  of  the  Orwell,  Benson  and  Sudbury  hills. 
The  black  slates  are  not  exactly  like  any  of  the  terrigenous  rocks 
that  the  writer  has  seen  among  the  hills  just  mentioned.  They 
also  appear  different  from  the  mud-colored  slates  or  shales  at  the 
west,  not  only  in  color,  but  in  the  fact  of  greater  metamorphism. 
On  the  strike  or  meridian  of  the  black  slates  farther  south  in 
Benson  at  Forbes  Hill,  however,  occur  the  light-colored,  siliceous 
phyllites  and  grits  so  common  at  the  east,  but  this  is  not  con- 
clusive of  similar  general  age  for  them  and  the  black  slates ;  for 
it  will  be  shown  that  the  probability  is  that  terrigenous  rocks 
have  been  overthrust  on  other  terrigenous  rocks  in  western  Ver- 
mont and  it  apparently  cannot  be  affirmed  whether  the  black 
slates  are  beneath  or  on  top  in  the  examination  of  a  surface 
section  of  such  an  overthrust.  It  seems  probable,  however,  that 
the  mud-colored,  friable  shales  are  of  different  age  from  the 
phyllites  at  the  east  in  Benson  village  and  eastward,  and  that 
they  may  belong  to  the  same  general  formation  that  contains  the 
black,  limy,  fossiliferous  slates  along  the  lake  shore  in  Orwell, 
and  also  some  of  the  Trenton  rocks.  If  this  is  so,  then  the  map 
of  Orwell  which  shows  the  slate  of  the  Orwell  hills  extending 
west  of  the  scarp  along  the  Benson-Orwell  road  should  differ- 
entiate among  the  slates  west  of  the  scarp  and  show  some  of 


mmi  mmti  nm  i  .vj^i 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  167 

them  in  the  character  used  to  represent  the  "Utica,"  just  as  was 
done  west  of  the  grist  jnill  farther  north.  On  such  an  interpreta- 
tion some  of  the  slates  would  be  part  of  the  mass  that  has  been 
overridden  and  therefore  probably  of  different  age  from  the 
other  terrigenous  rock.  It  is,  however,  not  easy  to  show  any 
sharply  dividing  line  at  the  present  surface. 

Continuing  the  section  eastward  from  Benson  village,  out- 
crops are  lacking  east  of  the  direct  road  from  Orwell  to  Fair- 
haven  along  the  road  to  "Spoke  Hollow"  or  "Howard  Hill  cor- 
ner." Due  north  of  this  road  in  the  high  hills  around  and  west 
of  Sunset  Lake  in  the  northern  part  of  the  township  are  phyllites 
and  quartzites  which  have  been  described  at  another  place,  and 
south  of  these  hills,  across  the  valley^s  of  the  head  streams  of 
Hubbardton  River,  are  entirely  similar  rocks  which  will  be  briefly 
mentioned  again  beyond.  Similar  rocks  are  found  on  Howard 
Hill. 

On  the  southeastern  slope  of  Howard  Hill  are  exposures  of 
limestone  bearing  strong  resemblance  to  rocks  which  a  little  way 
to  the  eastward  and  elsewhere  carry  Trenton  fossils.  A  half 
mile  east  along  the  road  through  Bangall  to  Hortonville,  on  each 
side  of  the  road  just  northeast  of  Hall's  corner,  are  ledges  of 
undoubted  Chazy  showing  the  lithological  characters  of  this  rock 
and  affording  good  samples  of  Strephochaetus  and  several  recog- 
nizable specimens  of  Maclurea  magna,  besides  fragments  of  other 
fossils. 

Eastward  from  these  ledges  of  Chazy,  about  half  a  mile, 
near  the  standpipe  of  the  Hortonia  Power  Company,  greatly- 
sheared,  blue  limestone  has  been  blasted  for  the  big  conduit  run- 
ning to  the  power  house,  and  still  further  east  between  Babbitt's 
corner  and  Hortonville,  north  and  south  of  the  road,  are  ledges 
of  faded  blue  limestone  which  give  evidence  of  arrangement  in 
undulating  folds  with  easterly  dip  which  is  sometimes  that  of 
stratification  and  sometimes  very  apparently  that  of  shearing  in 
westward  dipping  beds.  Fossils  are  numerous  on  the  weathered 
surfaces  and  include  many  small  spirals  and  numerous  sections 
in  the  plane  of  the  axes  of  the  spire  of  Murchisonia-  and  Pleuro- 
tomaria-\ike  gastropods.  In  its  fossil  contents  and  in  its  other 
characters  the  rock  is  like  that  which  at  the  north  and  northeast 
along  the  valley  of  the  Lemon  Fair  and  north  of  Horton  Pond 
carries  numerous  Trenton  fossils. 

Along  the  section  just  described  it  will  be  seen  that  at  the 
present  surface  there  is  wide  separation  by  terrigenous  rocks  of 
the  calcareous  rocks  near  the  lake  from  those  near  Bangall,  but 
that  the  latter  practically  join  the  limestones  of  the  valley  of  the 
Lemon  Fair,  and  actually  do  join  the  rocks  in  the  valley  along  the 
road  that  leads  from  Bangall  to  Abell's  corner.  Around  Horton- 
ville the  phyllite  formation  frequently  outcrops  through  the  lime- 
stone by  erosion  of  the  latter.     The  section  does  not  reveal  any 


168^  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Beekmantown  rocks  away  from  the  lake  region  at  the  present 
surface. 

The  field  relations  of  the  rocks  just  described  indicate  that 
the  calcareous  strata  east  and  west  of  Benson  village  lie  on  a 
formation  of  terrigenous  rocks.  That  these  latter  rocks  are  all 
of  similar  age  seems  improbable.  The  phyllites  on  which  rest 
the  Chazy-Trenton  rocks  near  Hortonville  are  entirely  similar 
to  those  of  some  of  the  Benson  hills  and  those  found  in  the  hills 
of  Orwell  and  Sudbury;  but  nearer  the  lake  the  Beekmantown- 
Chazy-( Trenton?)  beds  may  rest  in  part  on  phyllites  like  those 
at  the  east  and  in  part  on  very  different  slates.     See  figure  14. 

Some  observations  south  and  southeast  of  Benson  village. 
South  by  east  of  Benson  village  along  the  road  from  the  village 
through  O'Donnell  corner,  black  and  lighter-colored  phyllites  in 
the  association  that  has  been  so  frequently  mentioned  outcrop  at 
several  places.  At  O'Donnell  corner  they  occur  together  in  the 
same  ledge  in  the  exposures  near  the  dam.  These  rocks  con- 
tinue eastward  and  form  the  hills  east  of  the  road  from  Howard 
Hill  to  Fairhaven.  For  two  miles  along  the  Benson-Fairhaven 
road,  from  the  junction  of  the  Howard  Hill  road  with  it,  the  hills 
at  the  east  drop  by  a  high,  steep  scarp  to  the  plain  of  Hubbard- 
ton  River.  This  scarp  is  the  counterpart  of  those  along  the 
Benson-Orwell  road  north  of  Benson.  It  diminishes  in  height 
southward  and  the  Fairhaven  road  ascends  from  the  plain  and 
crosses  the  hill  to  Fairhaven.  Near  the  top  of  the  rise,  west 
of  the  road,  are  ledges  of  greatly-brecciated  blue  limestone. 
Fossils  have  been  destroyed,  but  the  rock  is  lithologically  like  the 
Trenton  as  observed  at  the  north.  The  apparent  dip  is  eastward. 
West  of  these  outcrops,  along  the  road  that  goes  over  Forbes 
Hill  to  Benson  village,  and  north  of  it,  are  other  ledges  clearly 
dipping  easterly  and  composed  of  gray  dolomitic  beds  and  light- 
blue  limestone.  The  blue  Hmestone  is  much  altered  and  sheared. 
One  much-weathered  specimen  which  was  identified  as  Maclurea 
magna  was  found  and  there  seems  little  doubt  that  the  beds  be- 
long to  the  Chazy.  Westward  and  between  these  outcrops  and 
Hubbardton  River  there  appear  to  be  other  ledges  of  Chazy, 
but  at  the  time  they  were  examined  circumstances  did  not  permit 
a  prolonged  study. 

Across  Hubbardton  River,  along  the  road  up  the  east  slope 
of  the  hill,  are  phyllites  like  those  in  the  hills  east  of  the  Fair- 
haven road  and  believed  to  be  the  continuation  of  them  beneath 
the  limestone  that  intervenes  and  to  have  been  exposed  by  the 
erosion  of  the  limestone.  They  continue  along  the  road  over 
Forbes  Hill  for  a  mile  and  a  half  where  the  limestones  appear  in 
the  fields  to  the  west  of  them  and  then  north  of  them  along  the 
road  towards  Benson  village.  The  latter  rocks  give  place  two 
and  a  half  miles  south  of  Benson  village  to  the  phyllites  again 
which  continue  along  the  road  towards  the  village.     Limestone 


REPORT  OF  THE  VERMONl'  STATE  GEOLOGIST. 


169 


was  also  noted  forming  detached  hills  in  the  plain  of  Hubbard- 
ton  River. 

The  exposures  just  described  south  of  Benson  village,  by 
a  somewhat  circuitous  route  it  is  true,  connect  the  limestones 
on  the  Hortonville  meridian  with  those  near  the  lake.  They 
carry  the  Chazy-Trenton  beds  nearer  the  lake  rather  than  the 
Beekmantown  away  from  it. 


Figure  13.  Writer's  interpretation  of  relations  east  of  Renson  Landing.  A, 
"Reekmantown,"  forming  a  low  abraded  anticline ; '  R,  Chazy,  separated 
from  A  by  a  brook  in  which  appear  shales  which  are  interpreted  as  ex- 
posures of  the  formations  that  have  been  overlapped  by  thrust ;  C,  prob- 
ably Trenton  ;  D,  black  phyllite,  probably  Lower  Cambrian,  interpreted 
as  unconformably  subjacent  to  the  Ordovician  limestones.  A  thrust,  1-2, 
has  cut  through  D  and  from  it  into  the  overlying  limestones  and  all  have 
been  driven  over  E,  Trenton- "Utica"  slates.  The  rocks  near  the  lake 
were  subsequently  dropped  by  normal  faults  as  shown. 

The  field  relations  of  all  the  exposures  now  described, 
though  briefly,  for  Benson  township  indicate  that  the  phyllite 
formation,  as  in  Orwell,  and  as  will  be  indicated  presently  as 
also  in  Sudbury  and  Brandon,  once  had  a  continuous  covering  of 
limestone  strata  which  was  either  thrust  or  deposited  upon  it. 
There  does  not  appear  to  be  any  essential  difference  in  the  ter- 
rigenous rocks  over  all  this  somewhat  extensive  area,  except  as 
indicated  above  for  certain  slates  at  the  west.  There  seems  tQ 
be  no  indication  that  the  limestone  appears  from  beneath  the 
phyllite  formation  on  account  of  folding  and  erosion  or  on  account 
of  thrust.  On  the  contrary,  the  various  areas  of  Hmestone  are 
either  purely  erosion  remnants,  or  thrust-erosion  remnants,  and 
whether  outliers  or  inliers  depends  upon  the  age  assigned  to  them 
and  to  the  terrigenous  formation  on  which  they  rest. 

Short  section  north  of  Benson  Landing.  Before  leaving  the 
Benson  area  it  seems  desirable  briefly  to  record  some  observations 
made  north  of  Benson  Landing. 

One  mile  north  of  the  landing,  at  Stony  Point,  siliceous 
limestone  of  arenaceous  texture  forms  a  cliff  rising  from  the 
lake  and  lies  nearly  flat.  Eastward  from  the  shore  surface  de- 
posits have  covered  the  hard  rock  to  a  great  extent,  but  through 
the  sugar  orchard  east  of  Sibbald's  cottage  and  eastward  to  the 
Chester  Bishop  place,  are  scattered  ledges  and  the  very  gentle 


170  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

dip  and  rock  exposures  indicate  the  northward  continuation  of 
the  rocks  and  structure  east  of  the  Landing.  In  the  northern 
section  within  a  distance  of  about  a  mile  were  seen  at  intervals 
going  eastward  small  exposures  in  the  following  sequence:  1,  at 
the  water's  edge  a  rather  coarse,  siliceous  dolomite;  2,  tough 
sandstone,  carrying  many  fragments  of  fossils  looking  like  trilo- 
bite  fragments ;  3,  siliceous  limestone  with  ridges  on  the  weathered 
edges ;  ^,  blue  limestone  "conglomerate"  with  irregular  frag- 
ments of  a  hue  slightly  different  from  that  of  the  matrix;  5,  layer 
with  numerous  whorls  on  the  weathered  surface ;  6,  drab  or  buff- 
colored  dolomites. 

From  this  sequence,  although  outcrops  were  usually  limited 
in  number  except  at  the  east,  it  was  concluded  that  this  flat 
arch  is  composed  largely  of  Brainerd  and  Seely's  Division  D, 
with  possibly  some  of  C  at  the  west  and  some  of  E  at  the  east 
where  the  dolomite  strongly  resembles  that  associated  with  the 
blue  limestone  of  the  Chazy.  So  far  as  observed  the  arch  was 
not  broken  or  eroded  to  expose  any  slates  through  it. 

EUTLAND  COUJfTT. 

Sndbnry  Township, 

(Brandon  topographic  sheet.) 

Topography.  This  township  includes  most  of  the  spur  of 
high  land  which  forms  the  northern  end  of  the  Taconic  range. 
On  the  west  and  northwest  the  spur  is  bounded  by  the  valley  of 
the  Lemon  Fair  River,  which  is  a  southward  extension  of  the 
Champlain  lowland  between  the  Taconic  hills.  On  the  east  and 
northeast  the  spur  is  bounded  by  the  low,  swampy  flood  plain  of 
Otter  Creek,  along  which  the  Champlain  lowland  merges  with  the 
Vermont  valley. 

The  spur  falls  off  gradually  in  altitude  northward  into  the 
low  schist  ridge  of  Whiting,  which  is  flanked  on  the  east  and 
west  by  limestone.  There  are  certain  structural  features  both 
within  the  spur  and  along  its  margins  which  will  be  described  in 
detail  beyond. 

General  geological  features.  As  one  passes  eastward  from 
the  lake  region  through  the  Taconic  range  towards  the  Green 
Mountains  the  confusion  in  field  relations  and  the  difficulty  of 
interpretation  increase.  The  field  worker  experiences  the  need 
of  multiplicity  of  detail  in  critical  relations  in  order  to  feel  at 
all  sure  of  his  views  of  structure  and  even  then  it  will  happen 
that  two  persons  will  arrive  at  quite  different  conclusions  with 
respect  to  the  meaning  of  presumably  critical  relations  or  will 
stress  quite  different  things  as  being  of  importance.  It  soon 
becomes  apparent  to  the  student  of  the  metamorphosed  and 
greatly  deformed  rocks  lying  east  of  the  lake  that  the  region 
must  be  viewed  more  or  less  as  one  grand  unit  in  order  to  see 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  I71 

into  the  meaning  of  its  smallest  part.  Recognition  of  the  direc- 
tion of  the  road  which  one  must  travel  to  get  anywhere  perhaps 
will  be  conceded  as  an  important  step  leading  towards  the  destina- 
tion. 

Noi'th  and  south  of  Sudbury  milage.  The  sheared  blue  lime- 
stones and  marble  and  associate^  gray  dolomite  in  the  valley  of 
the  Lemon  Fair  River  in  eastern  Orwell  township  that  have 
been  described,  continue  into  Sudbury  township  and  give  place 
eastward  to  the  terrigenous  rocks  of  the  Sudbury  hills,  which 
are  practically  continuous  northward  with  a  low  ridge  of  similar 
rocks  extending  northward  into  Whiting  township  and  south- 
ward join  with  the  entirely  similar  rocks  of  Hubbardton.  The 
map  shows  connection  across  the  ridge  of  the  limestone  of  the 
Lemon  Fair  valley  with  that  of  Otter  Creek.  Whether  one  showed 
the  area,  which  on  the  writer's  map  represents  a  surface  connec- 
tion of  the  limestones,  as  there  shown,  or  as  schist,  would  depend 
upon  what  outcrops  were  stressed,  as  will  be  seen  presently;  for 
it  appears  .that  schist  lies  beneath  limestone  in  the  area  and  also 
outcrops  through  it.  It  will  be  convenient  to  say  that  both  are 
practically  continuous,  which,  though  literally  impossible,  when 
so  stated  conveys  important  ideas.  The  schists  outcrop  every- 
where along  the  road  from  Webster's  corner  in  Sudbury  nearly 
to  Whiting  village,  also  westward  nearly  to  Ketcham  corner, 
where  they  appear  on  the  meridan  marked  by  the  marbles  and 
sheared  limestones  farther  south.  Eastward  they  extend  one- 
third  of  a  mile  from  Webster's  corner  along  the  road  to  Brandon 
and  are  then  interrupted  by  the  limestone  for  a  short  distance. 
At  this  interruption  the  limestone  is  really  a  calcareous  slate  as 
shown  in  pits  along  the  road  and  in  fields  nearby  and  might  be 
mistaken  for  the  schist  or  phyllite  formation  if  hastily  examined. 
A  little  farther  east  the  schist  appears  in  the  road,  east  of  the 
school  house,  but  is  again  bounded  by  the  limestone  north  and 
south. 

West  of  Sudbury  Hill  is  an  old  road  across  the  flats  that 
runs  from  the  village  to  Ketcham's  corner.  East  and  west  of 
this  old  road  are  detached,  knoll-like  patches  of  limestone  or 
"marble"  with  associated  gray  dolomite  projecting  through  the 
clay  of  the  old  "lake"  bottom  and  apparently  to  be  regarded  as 
practically  continuous  westward  beneath  the  clay  with  the  similar 
rocks  described  above  as  outcropping  in  the  banks  of  the  Lemon 
Fair;  but  whether  continuous  with  or  surrounded  completely  by 
limestone  beneath  the  clay,  or  whether  partly  surrounded  by 
schist,  could  not  be  determined  for  they  are  now  simply  islands 
in  the  clay.  These  exposures  show  varying  proportions  of  either 
sheared  blue  limestone,  or  "marble,"  with  gray  dolomite.  On 
the  .west  side  of  the  main  Sudbury  road,  on  the  west  slope  of  the 
hill  below  the  village,  the  rock  is  often  a  whitish  or  salmon-pink 
sheared  "marble"  and  this  and  the  rocks  in  general  along  the  old 


172  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

road  mentioned  are  entirely  similar  to  those  which  extend  around 
the  northern  end  of  the  schist  spur  and  join  with  others  at  the 
east.  Directly  west  of  Sudbury  church  the  sheared  "marble"  is 
overlain  by  a  mass  of  thick,  blocky,  gray  dolomite  through  which 
the  marble  peeks  at  places  and  the  structure  was  made  out  as 
probably  that  of  a  local  syncline  of  "marble"  holding  the  super- 
jacent dolomite. 

South  of  the  Sudbury  church  is  sheared  "marble"  and  asso- 
ciated dolomite  and  this  association  in  general  continues  along  the 
scarp  slope  east  of  the  Hyde  Manor  road  as  far  as  Hyde  Manor. 
South  of  the  Manor  the  "marbly"  rock  gives  place  apparently 
along  the  strike  to  light  blue  limestones  mostly  sheared  into 
slaty-looking  rocks  and  these,  except  for  an  occasional  tongue 
or  patch  of  schist  near  the  summit  of  the  slope,  and  with  obvious 
faults  and  flexures,  are  continuous  with  the  sheared  blue  lime- 
stones, dovetailed  with  tongues  of  schist  and  carrying  Trenton 
fossils,  north  of  Horton  Pond  and  extending  westward  across 
the  upper  valley  of  the  Lemon  Fair. 

Directly  east  of  Hyde  Manor,  along  a  brook  that  descends 
from  the  hill,  the  phyllite  formation  has  been  exposed  by  erosion 
of  the  Hmestone  and  is  continuous  eastward  at  the  surface  with 
that  of  Government  Hill.  South  of  the  road  from  Hyde  Manor 
over  the  hill  to  the  Huff  Pond  road  occur  patches  of  limestone 
surrounded  wholly  or  partly  by  schist  and  the  latter  outcrops 
through  the  limestone  at  the  summit  of  the  scarp  slope  just  west 
as  a  gray,  pyritiferous  rock  much  like  that  seen  in  the  valley  of 
Sugar  Hollow  Brook  east  of  Brandon  in  association  with  phyl- 
lites  quite  similar  to  those  of.  the  hill  east  of  Hyde  Manor. 

An  east-west  section  along  a  parallel  about  300  rods  north 
of  Sudbury  church  gives  sheared  blue  limestone  just  east  of  the 
stage  road,  which  is  succeeded  eastward  up  the  hill  slope  by 
phyllite,  and  this  in  turn  by  limestone.  But  along  this  section 
erosion  has  left  few  or  no  remnants  of  limestone  on  the  higher 
slopes,  and  eastward  over  the  hill  for  a  mile  and  a  half  all  is 
schist  or  quartzite. 

At  the  northern  end  of  the  Sudbury  spur,  about  a  mile 
northeast  of  the  church,  is  an  instructive  east-west  section  along 
which  erosion  has  produced  a  mutually  interrupted  series  of  out- 
crops of  limestone  and  schist,  as  now  exposed,  and  which  is  in- 
dicative of  what  was  probably  once  the  condition  over  all  the 
higher  portion  of  the  spur  to  the  southward. 

One  and  a  fourth  miles  north  of  Sudbury  church,  in  a  gulley 
beside  the  main  stage  road,  is  sheared  blue  limestone.  Eastward 
up  the  slope  this  is  succeeded  by  schist  which  is  the  northward 
continuation  of  similar  rock  on  the  northwest  slope  of  Govern- 
ment Hill  where  it  is  often  intermingled  with  patches  of  quartzite. 
The  schist  forms  a  scarp  which  is  topped  by  limestone.  The  scarp 
is  regarded  as  the  northward  expression  of  normal  displacements 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  173 

on  the  west  of  Government  Hill,  of  which  the  one  east  and  north 
of  Hyde  Manor  is  the  most  clearly  defined  at  the  present  time. 
The  Hmestone  topping  the  scarp  just  referred  to  is  a  slaty, 
sheared,  blue  rock  in  places  and  "marbly"  in  others.  It  is  suc- 
ceeded eastward  by  schist  with  contact  concealed,  but  with  the 
two  rocks  only  9  paces  apart.  Then  a  short  distance  eastward  is 
the  sheared  blue  limestone  again  with  "marbly"  aspect,  then  schist 
once  more,  then  sheared  blue  limestone  with  some  dolomite 
mixed  with  it,  then  schist,  and  once  more  sheared  "marble"  mixed 
with  dolomite,  then  "marble"  which  joins  at  the  present  surface 
with  extensive  exposures  of  similar  rock  lying  eastward  and 
northward  to  the  road.  On  the  map  the  phyllite  or  schist  is 
shown  dove-tailing  with  the  limestone  along  the  section  just 
described,  but  such  arrangement  is  somewhat  schematic.  The 
implication  is  that  the  calcareous  formation  is  superjacent  to  the 
terrigenous  rocks  as  is  the  case  in  the  areas  lying  to  the  west. 
This  relation  seems  to  be  capable  of  reasonable  proof  by  the 
means  so  far  employed  without  paying  much  special  attention  to 
differences  of  dip  and  strike  in  the  associated  rocks.  Many  areas 
of  the  "marbly"  rock  at  the  east  of  the  section  just  described  are 
pinkish  in  color  like  that  west  of  Sudbury  church.  Dolomite 
is  intermingled  with  it  at  various  places  and  it  passes  laterally 
into  blue,  sheared  limestone. 

East  of  the  section  just  described,  and  east  of  the  north- 
south  road  that  joins  the  Brandon  road  ("Otter  Creek  road"), 
near  the  school  house,  are  four  large,  conspicuous  hills  which  are 
composed  largely  of  sheared  Hmestones  and  marbles,  and  all 
show,  at  some  places  more  than  at  others,  gray  dolomite  resting 
on  the  blue  limestone  or  marble  in  patches  and  intermingled 
without  any  regularity. 

It  is  reasonably  apparent  that  the  north  end  of  this  spur  of 
the  Taconic  range  in  Sudbury  now  has  metamorphosed  limestones 
lying  on  the  schist  formation  and  that  the  latter  has  been  exposed 
at  many  places  by  erosion  of  the  limestone,  while  the  limestone 
has  been  preserved  from  erosion  at  certain  places  by  protection 
through  folding  or  faulting.  South  of  the  section  at  the  north  end' 
of  the  spur  which  was  just  described  to  demonstrate  these  rela- 
tions, and  to  show  that  the  conditions  prevailing  west  of  the  Sud- 
bury hills  also  occur  in  them,  limestone  has  not  been  found  by  the 
writer  within  this  spur  in  the  township  of  Sudbury,  except  east 
of  Hyde  Manor  along  the  lower  faulted  portion  of  the  western 
slope  of  Government  Hill,  where  the  limestone  which  tops  the 
considerable  scarp  east  of  the  Manor  extends  easterly  to  the  Huff 
Pond  road. 

The  question  of  the  age  of  the  sheared,  blue  limestones  and 
marbles  on  the  western,  northern  and  northeastern  slopes  of  the 
Sudbury  spur  apparently  cannot  be  readily  affirmed  from  fossils, 
as  most  of  these  rocks  are  extensively  altered.     None  was  found 


174  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

in  them  by  the  writer.  The  question  is  complicated  by  the  pres- 
ence of  disturbances,  some  of  which  seem  fairly  easily  defined  as 
to  character,  while  others  are  very  difficult  to  explain.  There 
are,  however,  some  considerations  which  serve  to  establish  the 
identity  of  some  of  the  limestone  on  the  basis  of  probability. 

The  fossiliferous  Trenton  limestones  in  the  southeastern  part 
of  Orwell  township,  as  discussed  above,  pass  eastward  across 
the  low,  hilly  land  between  the  head  stream  of  the  Lemon  Fair 
and  Horton  Pond  and  join  at  the  present  surface  with  the  sheared 
blue  and  slaty  limestones  south  of  Hyde  Manor,  while  these  pass 
northward  along  the  face  of  and  on  top  of  the  scarp  east  of  the 
Hyde  Manor  road  through  Sudbury  village  from  which  area, 
when  traced  northeastward,  they  join  with  the  limestone  expo- 
sures at  the  northern  end  of  the  Taconic  spur  and  when  traced 
northwestward  they  join  with  the  sheared  blue  limestones  and 
"marbles"  in  the  valley  of  the  Lemon  Fair.  The  latter  are  to 
all  appearances  the  northern  continuation  of  the  fossiliferous 
limestones  to  the  south  of  them.  Over  this  considerable  area, 
therefore,  these  various  rocks  may  seemingly  be  traced  with  un- 
important surface  interruptions  into  each  other.  Added  to  this 
is  the  important  fact  that  at  scores  of  places  these  various  rocks 
have  substantially  the  same  relation  to  an  underlying  schist- 
phyllite  formation,  which  is  throughout  essentially  the  same  in 
its  characters.  Moreover,  there  is  associated  with  all  these 
various  rocks  a  singularly  similar  gray  dolomite  which  has  held 
to  a  more  uniform  appearance  in  the  different  localities,  for  some 
jeaSon  or  other,  and  which  lies  on  the  fossiliferous  as  well  as  the 
metamorphic  rocks,  although  seemingly  more  abundant  at  the 
east.  Further,  the  strong  indications  of  normal  displacement 
on  the  west  of  Sudbury  Hill  afiford  explanation  of  any  apparent 
discontinuity  at  the  present  surface.  The  lithological  differences 
among  these  calcareous  rocks  require  explanation,  especially  on 
the  assumption  that  the  various  rocks  are  essentially  the  same; 
such  differences  might  be  seized  upon  to  show  that  the  rocks 
could  hardly  be  the  same.  But  any  effort  to  explain  the  differ- 
ences may  be  postponed  for  the  present. 

Description  of  an  irregular  or  composite  section  across  the 
northern  end  of  the  Taconic  range  passing  through  Government 
Hill.  The  section  begins  for  sake  of  completeness  at  the  Hyde 
Manor  road  and  extends  to  the  eastern  boundary  of  the  township 
of  Sudbury,  across  the  schist  formation. 

At  this  point  it  will  be  convenient  to  call  special  attention  to 
and  to  discuss  briefly  certain  lithological  differences  shown  by 
the  members  of  the  schist  formation.  Some  of  the  terrigenous 
rocks  making  up  this  formation  are  distinctly  schistose,  but  per- 
haps most  of  them  are  better  called  phyllites  than  schists  because, 
though  obviously  altered,  crystalline  rocks  and  while  generically 
speaking  they  are  schists,  they  are  prevailingly  rather  fine-grained 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  175 

and  do  not  show  their  minerals  conspicuously  when  viewed  with 
the  naked  eye,  except  where  they  carry  the  large  crystals  of 
pyrite  which  have  been  mentioned,  or  other  phenocrysts.  In  the 
older  descriptions  of  these  fine-grained,  micaceous  rocks  they 
were  called  "hydromica  schists."  Many,  perhaps  most,  of  these 
phyllites  are  black  and  man}?-  are  light-colored,  fissile  rocks, 
cleaving  somewhat  like  slate,  but  more  brittle  and  chipping  into 
many  small  pieces.  A  coppery-colored  stain  is  abundant  in  both, 
but  usually  more  apparent  on  the  lighter-colored  variety.  The 
pyrite  seems  to  be  much  more  characteristic  of  the  black  phyllites. 
It  occurs,  however,  in  some  of  the  other  terrigenous  rocks  of  this 
formation. 

True  slates  are  not  abundant  at  the  present  surface  over  the 
Sudbury  hills,  although  they  occur  there  and  in  the  Orwell  hills 
as  well.  They  have  not  been  found  good  enough  to  quarry 
profitably.  Occasionally  among  these  rocks  there  occurs  a  very 
black,  carbonaceous  phyllite,  rich  in  small  pyrite  grains,  and 
rather  restricted  in  its  lateral  and  horizontal  extent.  Quartzite 
is  abundant,  sometimes  in  scattered  small  patches,  but  at  other, 
places  continuous  at  the  surface,  or  practically  so,  over  con- 
siderable areas.  In  a  number  of  places  white  vein  quartz  in 
irregular  seams  and  patches  is  abundant  within  the  quartzite. 
Some  of  the  black,  pyritiferous  phyllites,  gritty  schistose  quartz- 
ites,  and  more  compact  or  massive  quartzites  are  indistinguishable 
from  similar  rocks  found  east  of  Brandon  in  the  ridge  west  of 
Sugar  Hollow  and  near  the  base  of  the  margin  of  the  plateau. 

While  there  is  thus  often  a  manifest  difference  in  general 
surface  aspect  of  ledges  in  close  proximity,  both  in  color  and 
lithology,  after  an  examination  of  hundreds  of  outcrops  over  the 
Sudbury  and  Orwell  hills  and  in  other  parts  of  the  Taconic  range, 
the  writer  has  failed  to  find  any  positive  criteria  by  which  to 
separate  one  from  another  on  the  basis  of  age.  The  structural 
relations  and  other  considerations  seem  to  afford  sufficient  ex- 
planation of  the  variations  seen  at  the  present  surface.  In  the 
high  scarps  on  the  west  of  the  hills  in  Orwell  and  northern  Ben- 
son, massive  quartzite  is  interbedded  with  black  phyllites  and 
other  rocks  which  could  not  be  satisfactorily  irrspected  on  these 
precipitous  scarps ;  but  which  together  had  an  aspect  very  similar 
to  that  given  by  a  surface  section  across  the  summits  of  the  ranges 
lying  east  and  similar  to  the  association  of  phyllite  and  quartzite 
east  of  Brandon. 

As  may  be  mentioned  again  beyond  there  appears  no  good 
reason  for  regarding  the  phyllites  along  the  low  ridge  that  ex- 
tends from  Sudbury  into  Whiting  as  different  from  those  in  the 
Sudbury  hills,  although  along  the  Sudbury- Whiting  road  the 
light-colored  variety  is  rather  in  predominance.  In  a  brook  two 
miles  northwest  of  Whiting  village  occurs  the   same  quartzite 


176 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 


with  its  nests  of  white  vein  quartz  that  is  so  conspicuous  on 
Government  Hill. 

One-half  mile  north  of  Hyde  Manor  and  east  of  the  stage 
road  is  a  scarp.  The  steepest  portion  of  the  face  near  the  top 
is  a  sheared  "marble."  This  continues  over  the  summit  and 
eastward  is  covered  at  places  with  the  gray  dolomite.  The  cal- 
careous rocks  extend  from  the  scarp  eastward  for  about  one-third 
of  a  mile  to  the  Huff  Pond  road.  At  the  base  of  the  scarp  at 
places  near  Hyde  Manor  the  dolomite  has  a  position  that  might 
suggest  an  interbedded  relation  to  the  "marble,"  but  as  the  super- 
jacent position  of  the  dolomite  is  more  apparent  the  relations  at 
the  Manor  are  interpreted  as  due  to  faulting  as  shown  in  figure  14. 


w 

E 

F 

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o 

V 

QOARTJJITC-   SCHIST 
FORMATION 

Figure  14.  Section  just  north  of  Hyde  Manor,  somewhat  generalized  as  to 
attitude  of  beds,  showing  gray  dolomite  as  probably  faulted  with  sheared 
limestone,  which  produces  appearance  of  being  interbedded.  The  cal- 
careous rocks  are  shown  as  being  underlain  by  the  quartzite-schist 
formation  of  the  Sudbury  hills. 


A  little  south  of  the  section  as  just  begun,  along  the  cross- 
road from  the  Manor  to  the  Huff  Pond  road,  and  also  east  of  the 
main  road  from  Sudbury  village  to  the  pond,  on  the  western  slope 
of  Government  Hill,  are  black  phyllites  with  bedding  unusually 
distinct  and  striking  nearly  east  and  west,  N.  about  70°  E.,  and 
farther  up  the  slope  near  the  summit  thick-bedded  quartzite 
shows  much  disturbance  from  the  prevailing  strike  of  the  rocks 
roundabout.     A  reading  here  gave  N.  70°  W. 

The  surface  rock  on  the  western  slope  of  Government  Hill 
is  prevailingly  a  blackish  phyllite,  with  some  patches  of  quartzite, 
but  the  latter  forms  most  of  the  ledges  north  and  south  along 
the  summit  of  the  hill,  and  in  places  carries  much  vein  quartz  in 
irregular  seams  and  bunches. 

Government  Hill  descends  over  quartzite  by  a  gentle  slope 
of  irregular  surface  on  the  east  about  150  feet  through  a  distance 
of  less  than  one-third  of  a  mile.  Then  comes  an  ill-defined 
scarp,  which  does  not  appear  on  the  topographic  map,  with  the 
black  phyllite  at  its  base  and  quartzite  forming  the  higher  portion 
and  summit.  Eastward  this  hill  descends  over  quartzite  by  irreg- 
ular surface  to  a  swamp  with  a  sharp  scarp  facing  west  on  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  177 

t 

east  of  the  swamp  and  with  the  black  phyllite  at  the  base  and 
quartzite  again  at  the  succeeding  summit.  Then  another  east- 
erly slope  to  a  swamp  with  another  scarp,  sharper  if  anything 
than  those  just  mentioned  and  exhibiting  similar  geological  rela- 
tions. 

East  of  the  eastern  slope  of  Government  Hill,  the  section  as 
thus  far  described,  is  either  through  a  dense,  swampy  tangle 
or  thick  woods  and  very  difficult  to  travel  se,  but  while  the  ledges 
are  much  covered  with  decaying  vegetation  the  succession  can 
be  made  out. 

At  the  east  of  the  spur  in  the  high  hill  north  of  Dolan's  house, 
two-thirds  of  a  mile  north-northeast  of  Landon's  corner,  the 
quartzite  seems  thinner  than  farther  west.  This  hill  has  a  sharp 
scarp  on  the  east  which  is  clearly  visible  from  the  road  running 
northerly  from  "Pond  Hole"  school  house.  Between  the  base  of 
the  scarp  and  the  road  are  abundant  ledges  of  the  black  phyllite 
with  patches  of  quartzitic  graywacke  and  some  of  the  lighter- 
colored  phyllite  intermingled  with  it.  The  map  shows  the  fault 
marked  by  the  scarp  just  described.  The  schist  has  been  dropped. 
North  and  south  on  the  downthrow  side  it  gives  place  at  the 
surface  to  exposures  of  sheared  blue  limestone  and  dolomite.  At 
the  north  the  latter  lie  now  in  great  confusion  and  in  places  near 
the  schist  are  much  mashed  and  broken.  Eastward  across  the 
road  and  brook  the  phyllite  is  succeeded  by  sheared  and  foliated 
"marble,"  or  blue  limestone,  and  associated  dolomite. 

From  the  scarp  just  described  a  probable  fault  extends 
northwesterly  between  the  phyllite  and  limestone  towards  the 
northern  end  of  the  Sudbury  spur.  This  is  marked  by  a  scarp 
for  some  distance,  with  a  swamp  at  its  base.  The  limestones  east 
of  the  north-south  fault  just  mentioned  are  on  a  meridian  oc- 
cupied by  "Long  Swamp"  at  the  north;  while  those  north  of 
the  probable  fault  running  northwesterly  lie  on  the  meridian 
of  and  are  identical  with  those  which  have  been  described  as 
forming  the  high  hills  northeast  of  the  Sudbury  spur. 

From  the  facts  now  recited,  of  the  occurrence  east  of  Sud- 
bury church  along  the  strike  of  the  sheared  "marble"  at  Hyde 
Manor  of  black  phyllite  like  that  east  of  this  marble  at  -the  base 
of  Government  Hill,  and  of  the  occurrence  of  similar  phyllite 
along  the  strike  of  the  "marble"  west  of  Burr  Pond  and  north  of 
Horton  Pond,  and  of  field  relations  in  Sudbury  village  and  north- 
east of  it,  as  well  as  at  other  places,  it  is  apparent  that  the  phyl- 
lite is,  along  the  margins  of  the  Sudbury  hills,  subjacent  to  lime- 
stones that  can  be  rather  satisfactorily  traced  into  one  another  at 
the  present  surface  and  which  present  similar  features  and  asso- 
ciations. And  a  field  examination  leaves  a  strong  impression, 
almost  no  doubt,  that  the  different  members  of  the  terrigenous 
formation  are  components  of  a  formational  unit. 


173  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Composite  section  from  the  phyllites  of  southern  Orwell 
across  the  Taconic  range  to  Otter  Creek  in  Brandon.  This  sec- 
tion, like  the  preceding  one,  is  a  broad  band  or  belt  from  west  to 
east. 

Beginning  in  the  phyllite  formation  in  southern  Orwell,  for 
sake  of  completeness,  the  section  passes  from  these  phyllites  over 
a  band  of  limestone,  which  is  the  northern  extension  of  the  Chazy- 
Trenton  rocks  of  Bangall  in  Benson  township,  with  some  irregular 
outcroppings  of  phyllite  through  the  limestone,  then  over  phyl- 
lites which  are  the  northern  extension  of  those  in  Hortonville, 
then  over  a  succession  of  limestone  and  phyllite  bands  dovetailed 
in  with  each  other,  the  limestones  carrying  probable  Trenton 
fossils,  to  the  phyllites  west  and  north  of  Burr  Pond.  The  black 
and  associated  light-colored  phyllites  forming  the  hill  north- 
northwest  of  Burr  Pond  are  succeeded  eastward  at  the  eastern 
base  of  the  hill  by  massive  quartzite  with  prominent  ledges  just 
east  of  the  brook  that  feeds  Burr  Pond,  between  the  brook  and 
the  road.  Across  the  road  is  a  softened  scarp,  facing  west,  then 
for  a  mile  schists  with  patches  of  quartzite  to  another  scarp  that 
faces  east  and  at  the  base  of  which  is  the  sheared,  blue  limestone 
extending  south  of  "Pond  Hole."  This  scarp  is  the  southward 
continuation  of  that  which  was  described  in  the  preceding  section 
as  bounding  the  phyllite  and  quartzite  formation  on  the  east. 
The  fault  which  this  scarp  marks  can  be  followed  southward 
with  diminished  scarp  and  passes  just  east  of  High  Pond,  about 
two  miles  south  of  "Pond  Hole."  The  map  does  not  attempt  to 
show  a  number  of  scarps,  which  presumably  mark  fault  lines 
through  these  hills,  because  the  writer  wished  to  avoid  a  preju- 
dicial impression  which  often  comes  from  seeing  many  such 
features  represented  on  a  map  whose  area  is  so  small  in  compari- 
son with  that  of  the  actual  territory  pictured.  An  examination 
of  the  region  would  be  sufficient  to  show  how  much  these  rocks 
have  been  disturbed  and  the  extent  to  which  their  present  surface 
succession  and  arrangement  may  be  explained  by  disturbance. 

Taking  up  the  description  at  a  point  one-fourth  of  a  mile 
north  of  High  Pond,  along  the  fault  line  just  mentioned  as  extend- 
ing south  of  "Pond  Hole,"  the  section  eastward  is  over  black 
phyllites  on  the  west  slope  of  the  hill  called  "Stiles  Mountain"^ 
on  the  map,  then  over  massiX^e  quartzite  in  prominent  ledges 
through  the  woods  along  the  east  slope  to  the  road,  then  across 
the  road  and  on  phyllites  and  quartzites  over  a  succession  of 
steep,  scarp-like  slopes  facing  west  and  gentle  ones  facing  east, 
including  those  of  Stiles  Mountain  proper,  for  a  mile  and  a  half 
to  an  old  wood  road.  East  of  this  road  on  the  west  of  Castle 
Mountain  is  a  very  steep  scarp  at  whose  base  a  brook  runs 
northerly.  In  the  bed  of  this  brook,  perhaps  100  rods  from  its 
junction   with  another  brook,   massive   quartzite   rests   on  black 

1  The  name   Stiles  Mountain,   according  to  the  residents,   really   belongs 
to  the  second  high  hill  east  of  this  one. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  179 

phyllite  on  the  downthrow  side  of  the  fault,  which  is  marked  by 
the  scarp  under  which  the  brook  flows.  The  west  scarp  of  Castle 
Mountain  ascends  oyer  phyllites,  which  are  succeeded  at  the 
summit  and  down  the  eastern  slope  of  the  mountain  by  phyllites 
and  quartzite.  Midway  down  the  eastern  slope  are  patches  of 
gray,  siliceous  dolomite  of  arenaceous  texture.  The  phyllites 
with  quartzite  continue  to  the  base  of  the  hill  and  are  succeeded 
eastward  at  the  edge  of  the  valley  by  marble  and  blue  limestone 
with  associated  gray  dolomite.  Along  the  section  just  described 
the  light-colored  phyllites  are  frequent  at  more  or  less  regular 
intervals,  but  without  any  defined  order. 

Over  the  high  hills  along  the  southern  boundary  of  Sudbury, 
from  Horton  Pond  to  the  valley  of  Otter  Creek,  which  were  sur- 
veyed with  care,  no  Hmestone  was  found  by  the  writer  except  the 
siliceous  dolomite  mentioned  as  occurring  in  patches  on  the  east- 
ern slope  of  Castle  Mountain.  Further  evidence  that  the  lime- 
stone once  rested  on  the  terrigenous  rocks  is  however  obtained 
from  relations  shown  along  the  valley  of  the  brook  that  flows 
east  in  the  hollow  north  of  Stiles  Mountain  (proper)  and  Castle 
Mountain  to  join  Otter  Creek.  Along  this  valley,  as  shown  on 
the  map,  and  separated  by  the  phyllites  and  quartzites  from  the 
limestones  of  the  valley  of  Otter  Creek,  and  surrounded  by  the 
terrigenous  rocks,  are  patches  of  sheared,  bluish  marble.  The 
valley  of  the  brook  is  presumably  a  small,  east-west  trough- 
faulted  basin  separating  the  hills  north  and  south  of  it,  and  the 
limestone  has  been  dropped  between  them. 

The  road  from  Bressee  Mill  to  Brandon,  a  half  mile  south 
of  the  Dean  farm,  skirts  the  eastern  base  of  a  scarp  in  greatly 
sheared  and  contorted  marble,  which  at  the  top  of  the  scarp  rests 
on  quartzitic  schist,  while  south  of  this  scarp  on  both  sides  of  the 
road  to  Bressee  Mill  are  ledges  of  massive  quartzite.  There  is 
a  scarp  running  west-northwest  from  the  road  south  of  Dean's 
place  and  which  extends  from  the  edge  of  the  Otter  Creek  valley 
to  the  embayment  which  is  shown  on  the  map  as  bounded  rather 
symmetrically  by  fault  displacements.  This  scarp  probably  marks 
a  normal  displacement  and,  although  phyllite  occurs  on  the  down- 
throw side,  it  substantially  separates  limestone  on  the  north  from 
the  terrigenous  rocks  of  the  hills. 

The  embayment  mentioned,  in  which  the  limestone  now  ex- 
tends southward  at  the  surface  between  higher  masses  of  phyl- 
lite, is  bounded  at  the  south  by  another  scarp  along  the  high  ten- 
sion line  of  the  Hortonia  Power  Company,  just  north  of  which 
is  a  considerable  swamp.  South  of  these  faults  as  just  described 
as  bounding  the  phyllite  hills  on  the  north,  the  limestone  has  been 
eroded  on  the  upthrow  side,  except  as  shown  on  the  map.  North 
of  them  the  limestone  has  been  preserved,  as  shown,  by  down- 
faulting.  On  the  northeast  the  Taconic  hills  are  thus  separated 
from  the  low  land  west  of  Otter  Creek  by  well-marked  normal 
fault  displacements. 


180  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

.^   KUTLAND  COUNTY. 

Brandon  Township. 

(Brandon  topographic  sheet.) 

Topography.  The  short  spur  of  the  Taconic  range  which 
includes  "Stiles  Mountain"  and  "Castle  Mountain,"  whose  geology 
was  described  under  Sudbury,  really  belongs  in  Brandon  township. 
Bordering  this  spur  on  the  east  is  the  low,  level  flood-plain  of 
Otter  Creek  which  extends  into  the  northwestern  part  of  the 
township  and  there  is  largely  occupied  by  extensive,  wooded 
swamps. 

Except  for  a  short  distance  near  Brandon  the  Rutland  R.  R. 
follows  the  eastern  margin  of  the  plain.  At  various  places 
ledges  emerge  from  the  plain  as  detached  knolls,  some  of  which 
are  of  considerable  size;  but  for  the  most  part  along  the  creek 
the  hard  rock  is  hidden. 

Along  the  eastern  edge  of  the  plain  are  low  hills  which  offer 
nearly  continuous  exposures.  On  the  whole  the  land  rises  east- 
ward to  form  a  somewhat  rolling  upland  which,  with  some  inter- 
ruptions due  to  ancient  dissection  of  the  rock  surface,  passes  into 
the  foothills  of  the  Green  Mountain  plateau.  The  Neshobe 
River  and  other  streams  have  in  recent  times  terraced  an  old  sand 
plain  that  marks  a  period  of  glacial  flooding  or  a  submergence 
of  the  old  rock  valleys  among  the  hills  east  of  Brandon  village. 
East  of  these  streams  the  land  rises  more  rapidly  to  the  western 
edge  of  the  plateau,  but  east  of  Brandon  a  ridge  of  intermediate 
elevation  is  separated  from  the  steep  scarps  that  border  the 
plateau  by  the  valley  of  Sugar  Hollow  Brook.  In  general,  how- 
ever, a  strip  of  hilly  and  mountainous  land  about  two  miles  wide 
extends  in  a  north-south  direction  through  the  eastern  part  of 
the  township. 

General  geological  features.  In  Brandon  township  many  of 
the  rocks  are  marked  and  masked  by  still  greater  metamorphism 
than  that  shown  by  the  rocks  of  Sudbury.  But  this  feature  is 
not  true  of  all.  In  this  township  appears  a  series  of  beds  that 
has  not  been  identified  in  Sudbury  and  is  the  northern  con- 
tinuation of  the  "interbedded  series"  of  the  Lower  Cambrian 
that  will  be  discussed  in  connection  with  different  parts  of  the 
Vermont  valley  at  the  south.  In  their  well-preserved,  bedded 
character  and  in  other  ways  these  rocks  are  in  contrast  to  most 
of  the  other  calcareous  rocks  of  the  Brandon  area,  which,  as 
exposed  both  at  the  surface  and  in  the  quarries,  give  evidence  of 
great  dynamic  stresses  in  the  flow  structures  which  they  exhibit 
and  in  the  obvious  crushing  and  crystallization  which  they  have 
undergone. 

With  the  terrigenous  rocks  in  many  cases  there  does  not 
appear  to  be  distinguishable  difference  between  those  in  the  Sud- 
bury-Orwell  hills  and  similar  types  lying  east  of  Brandon  village ; 


^  -  >     j^ 

~    X    ~  ^    ~ 


'—    Ti         _    i 


3=^-2 


—         X   — 

^  •-  a:  I  —  - 


:^T,?^^  = 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  Igl 

but  in  the  scarps  of  the  western  edge  of  the  plateau  and  at  other 
places  along  its  edge,  quartzite  and  arkose  have  sometimes  been 
sheared  into  more  or  less  foliated  rocks. 

General  relations  west  of  Brandon  village.  The  sheared 
"marbly"  rocks  and  sheared  blue  limestone  with  associated  gray 
dolomite  which  compose  the  conspicuous  hills  in  the  northeastern 
part  of  Sudbury  township  in  some  cases  lie  in  faulted  position 
against  the  rocks  that  underlie  the  plain  of  Otter  Creek,  along 
which  a  surface  area  two  miles  wide  with  few  exposures,  sepa- 
rates the  rocks  on  the  west  from  those  on  the  east  of  the  creek, 
although  there  are  a  few  detached  outcrops,  or  islands,  which 
serve  in  a  measure  to  bridge  the  gap.  The  easterrimost  of  these 
islands  is  at  the  southern  extremity  of  "Long  Swamp"  and  lies 
on  the  meridian  which  farther  north  marks  the  western  edge  of 
practically  continuous  surface  exposures  northwest  of  Brandon, 
which  edge  is  two  miles  east  of  the  meridian  along  which  lie 
the  conspicuous  hills  of  Sudbury  township  mentioned  above. 

South  of  "Long  Swamp"  and  north  of  the  fault  at  the  north- 
ern end  of  the  Taconic  hills  which  lie  southwest  of  Brandon 
village,  a  continuous  surface  section  from  west  to  east  spans 
the  distance  between  the  two  meridians  and  joins  fairly  closely 
with  other  exposures  which  carry  the  limestones  to  the  meridian 
of  Brandon  village,  while  farther  south  detached  exposures, 
similar  to  those  at  the  north,  outcrop  in  the  plain  of  Otter 
Creek,  which  owing  to  the  course  of  the  creek  is  here  two  miles 
or  more  east  of  the  plain  in  the  northwestern  part  of  the  town- 
ship, and  carry  the  section  in  limestone  to  a  meridian  which 
passes  a  mile  east  of  Brandon  village. 

The  above-described  relations  may  assist  somewhat  in  under- 
standing the  geological  features  around  Brandon  village. 

The  calcareous  rocks  of  the  islands  along  the  plain  of  Otter 
Creek  and  along  the  continuous  east-west  exposiire  south  of 
"Long  Swamp,"  except  some  rocks  which  will  be  mentioned 
later,  are  entirely  similar  to  those  which  have  been  described  for 
the  northern  end  of  the  Taconic  spur  in  Sudbury.  Making  due 
allowance  for  such  disturbances  as  these  rocks  have  experienced 
since  their  present  general  relation  to  the  phyllite  formation  had 
been  established,  it  has  seemed  possible  to  trace  rather  satis- 
factorily the  counterparts  of  the  fossiliferous  beds  on  the  west 
side  of  the  Taconic  spur  around  its  northern  end  into  the  Brandon 
area.  Two  considerations  seem  especially  to  warrant  the  pro- 
priety of  such  procedure : 

\.  The  invariable  occurrence  of  a  similar  association  of  gray 
dolomite  with  marble  or  blue  limestone  in  all  fairly  extensive  ex- 
posures. 

2.  The  fact  that  if  we  view  the  transition  area  from  Sud- 
bury into  Brandon  broadly,  that  is,  so  as  to  include  an  east-west 
section  as  wide  as  the  township  of  Brandon  is  long  from  north 


182  REPORT  OF  THE  VERMONT  STATE  GEOLOQIST. 

to  south,  we  have  rocks  on  the  eastern  side  of  the  Taconic  spur 
having  the  same  relation  to  the  terrigenous  formation  as  that 
which  obtains  on  the  western  side  and  at  the  northern  end,  and 
not  to  be  disguised  by  any  faulting  which  has  occurred  on  the 
east. 

The  latter  consideration  seems  to  give  further  indication  that 
the  same  terrigenous  formation  that  composes  the  Taconic  spur 
is  present  at  depth  beneath  the  marbles  and  their  associated  dolo- 
mite beds  of  the  Champlain  lowland  around  Brandon  village. 
On  such  an  assumption  it  becomes  easy  to  account  for  the  simi- 
larity of  the  terrigenous  rocks  east  of  Brandon  to  those  of  the 
Taconic  spur  and  to  support  certain  ideas  of  the  down-faulted 
character  of  the  Vermont  valley  around  Brandon  and  in  other 
places  which  will  be  offered  later.  If  such  an  assumption  should 
prove  plausible  it  must  have  far  reaching  significance  in  the  inter- 
pretation of  the  structure  of  the  region. 

The  gray  dolomite  which  has  so  frequently  been  mentioned 
as  occurring  in  association  with  the  sheared  blue  limestone  or 
the  marble  rocks  west  of  Brandon  seems  to  be  quite  distinct  from 
any  member  of  the  interbedded  series  which,  as  will  be  described 
later,  consists  of  interbedded  dolomitic  limestones,  calcareous 
quartzites,  and  quartzites,  and  perhaps  other  dolomite  not  strictly 
interbedded,  like  those  occurring  throughout  the  Vermont  valley ; 
and  this  distinction  holds  even  in  those  places  where  the  inter- 
bedded series  also  is  now  clearly  present  above  the  marble. 

In  the  Brandon  area  there  are  exposures  in  which  this  gray 
dolomite  is  associated  with  a  dove-colored  rock,  which  is  striped 
precisely  like  the  Chazy  rock  seen  at  Bangall  in  Benson  township, 
where  it  carries  well-defined,  probably  middle,  Chazy  fossils, 
and  like  that  seen  west  of  Bennington  in  southern  Shaftsbury, 
and  elsewhere.  One  of  the  places  near  Brandon  where  this 
striped  rock  may  be  seen  to  good  advantage  is  one  and  a  half 
miles  north  of  the  village,  about  300  rods  west  of  the  old  race 
course.  The  rock  here  is  so  greatly  altered  that  all  traces  of 
organic  remains  have  been  obliterated  and  do  not  appear  with 
any  definite  characters  even  in  weathered  outcrops.  The  stratum 
showing  this  association  continues  southward  to  the  angle  of  the 
roads  and  across  the  west  road.  It  also  occurs  a  mile  south, 
west  of  the  village,  north  of  the  "Otter  Creek  road,"'  and  at  other 
places  west  of  the  village. 

This  association  had  also  been  noted  at  places  in  Sudbury, 
and  at  other  places  less  distinctly  in  the  Brandon  area ;  but  what 
now  seems  its  probable  significance  was  not  grasped  until  the 
examination  of  the  Brandon  area  was  well  under  way  and  until 
the  Brandon  region  had  been  reviewed  in  the  light  of  relations 
which  are  shown  at  the  west. 

If  this  association  of  dove-colored  rock  and  gray  dolomite 
is  the  Chazy,  as  now  seems  to  the  writer  likely,  it  appears  to  be 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  183 

significant  that  it  so  often  lies  apparently  on  the  marble,  or 
above  the  sheared  blue  limestone,  as  the  case  may  be.  In  the 
vicinity  of  Brandon,  except  where  the  interbedded  series '  of 
dolomite  and  quartzite  has  overlapped  it,  the  dove-colored  rock 
and  its  dolomite  roughly  alternate  across  the  strike  with  the 
marble,  with  the  result  that  each  of  these  strata  forms  an  indis- 
tinct band  or  "vein"  running  somewhat  parallel  with  the  other 
north  and  south.  A  greater  width  of  the  marble  "veins"  is  now 
seen  along  the  meridians  where  this  rock  is  quarried. 

The  marble  bands  are  not,  however,  homogeneous  in  their 
composition.  Every  quarry  of  any  size  in  this  area  shows  some 
dolomite,  either  on  top  of  the  marble  or  as  infolded  blocks  or 
other  involved  fragments  in  the  quarry  rock.  Where  these 
dolomitic  or  "flinty"  masses  are  discovered  in  the  course  of  quar- 
rying they  usually  halt  the  work  at  that  point  and  drive  the 
quarrying  in  a  new  direction.  In  Huntley's  quarry  at  Leicester 
Junction,  where  the  rock  is  burned  for  lime,  pink  marble  just 
like  that  northeast  of  the  Sudbury  spur  has  sheared  each  side 
of  a  huge  block  of  dolomite  which  shows  in  the  north  a.nd  south 
faces  of  the  quarry.  This  dolomite  is  often  a  drab-colored  rock 
and  frequently  occurs  in  close  association  with  interbedded  dolo- 
mites and  quartzites.  In  the  quarries  generally  all  bedded  struc- 
ture is  greatly  obscured  or  obliterated  and  profound  dynamic 
effects,  such  as  mashing,  flowage  and  crystallization,  are  every- 
where manifest. 

The  explanation  of  the  relations  of  the  gray  dolomite  and  its 
associated  dove-colored  rock  to  the  marble  around  Brandon  seem- 
ingly must  account  for  the  present  apparent  superposition  of  the 
former  in  so  many  places  on  the  assumption  that  the  former  is 
Chazy  and  the  latter  probably  Trenton.  The  agency  of  reverse 
faulting  or  thrusting  at  once  comes  to  mind.  The  effect  of  such 
deformation  would  be  to  elevate  the  Chazy  against  the  younger 
rock  and  carry  the  former  over  the  latter.  If  this  deformational 
process  was  repeated  at  intervals  across  what  is  now  the  general 
line  of  strike  of  these  rocks  the  immediate  effect  would  be  to 
ease  the  stress,  at  least  for  a  time,  which  was  felt  by  the  mass  of 
rocks  in  which  these  ruptures  occurred  and  to  heap  the  rocks  by 
piling  some  on  others.  Account  must  be  taken  of  the  possible 
former  presence  of  other  limestone  strata  beneath  what  is  called 
"Chazy"  and  also  of  strata  above  what  is  called  "Trenton"  at  the 
time  of  this  postulated  faulting.  The  rough  regularity  of  the 
relations  between  the  two  strata,  as  now  exposed,  might  be  ac- 
counted for  on  the  basis  of  certain  primary  structural  relations 
which  the  mass  of  which  they  were  a  part  had  to  the  stress  sus- 
tained by  it. 

Certain  assumptions  have  clearly  been  made  as  the  premises 
for  the  considerations  just  offered ;  but  it  will  be  remembered  that 
effort  was  made  to  give  a  foundation  of  probability  to  the  ages 


184  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

of  the  rocks  in  the  Brandon  area  which  have  been  discussed  by 
tracing  the  less  altered  rocks  at  the  west  into  them  through  more 
or  less  continuous  surface  exposures  and  by  careful  lithological 
correlation  and  by  general  field  relations. 

The  greater  metamorphism  of  the  rocks  at  the  east  in  Bran- 
don might  be  explained  as  due  to  several  factors.  These  rocks 
might  have  been  involved  in  primary,  or  at  least  antecedent, 
relations  different  from  those  at  the  west  at  the  time  they  came 
under  kinetic  stresses;  or  they  might  have  been  subjected  to  con- 
tinued or  repeated  compression  after  new  conditions,  such  as  a 
loading  due  to  overthrusting,  had  been  imposed ;  or  they  might  be 
thought  of  as  having  been  involved  in  the  zone  of  most  severe 
crushing  in  the  region.  These  rocks  at  the  east  give  evidence  of 
having  sustained  pressure  under  confinement,  whether  this  con- 
dition was  a  special  one  present  only  at  the  east  when  the  rocks 
at  the  west  were  sheared  into  their  present  condition,  or  whether 
it  was  a  condition  antecedent  or  subsequent  to  the  operation  of 
those  stresses  which  sheared  the  rocks  at  the  west. 

The  deformational  structure  of  the  limestones  west  of  Bran- 
don, as  far  east  at  least  as  the  present  western  margin  of  the  "in- 
terbedded  series,"  is  that  of  shearing  chiefly.  This  shearing  seems 
to  increase  eastward  towards  the  areas  in  which  the  rock  has 
taken  on  the  characters  which  are  shown  by  the  marble  of  the 
Otter  Creek  valley.  It  is  practically  along  the  meridian  on 
which  falls  the  present  eroded  western  margin  of  the  "inter- 
bedded  series"  west  of  Brandon  village  that  the  commercial 
marble  runs  out  westward  at  the  surface  southwest  of  Brandon, 
and  even  the  quarries,  including  the  "old  Goodell  quarry,"  opened 
at  this  western  limit  south  of  the  "Long  Swamp  road,"  one- 
fourth  of  a  mile  east  of  M.  F.  Phillip's  house,  were  soon  aban- 
doned. One  of  these  quarries  shows  very  well  the  gray  dolomite 
folded  as  a  small  patch  with  the  dove-colored  rock  and  both  of 
these  driven  as  one  mass  over  the  marble.  The  latter  shows  its 
bedded  structure  much  more  distinctly  than  does  the  more 
severely  crushed  rock  farther  east,  which  is  a  feature  that  falls 
in  line  with  other  characters  to  mark  a  transition  zone  between 
the  rocks  at  the  west  and  those  of  Otter  Creek  valley.  South  of 
the  "Long  Swamp  road,"  between  it  and  M.  F.  Phillip's  place 
and  about  one-fourth  of  a  mile  southeast  of  Martin  Ketcham's 
place,  is  a  clifif  in  the  limestone  facing  north.  In  the  face  of  the 
cliff  great  irregular  blocks  of  limestone  rest  against  others  along 
irregular  contacts  and  where  two  come  together,  big  chunks  fall 
away,  while  the  rock  is  broken  throughout  into  small,  irregularly 
shaped  pieces,  usually  with  good  faces,  but  with  much  irregularity 
of  shape,  and  the  whole  mass  indicates  beyond  a  doubt  that  it 
has  been  greatly  crushed  and  brecciated,  but  apparently  not 
under  the  same  degree  of  confinement  as  the  marble  and  other 
rocks   farther  east.     The   surface  exposures  roundabout,  parti- 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  185 

cularly  to  the  southward,  show  intermingled  dove-colored  rock 
and  its  gray  or  chamois-colored  associate,  with  occasional  patches 
of  marble.  Each  is  deformed  by  shearing,  a  feature  which  the 
dolomite  shows  least,  and  all  are  much  disturbed  and  involved 
with  each  other. 

A  number  of  considerations  make  it  appear  that  there  is  a 
progressively  increasing  metamorphism  from  west  to  east  in  the 
calcareous  rocks  in  passing  from  Sudbury  into  Brandon ;  but 
whether  the  relatively  moderate  shearing  shown  by  the  rocks  at 
the  west  was  a  structure  antecedent  in  the  rocks  at  the  east  to 
the  greater  deformation  now  shown  by  them,  or  whether  the 
two  are  different  expressions  of  stresses  acting  at  the  same  time 
but  under  different  conditions  is  a  question  involving  other  con- 
siderations. In  general  it  appears  that  all  the  various  calcareous 
rocks  ^which  have  just  been  described,  were  obliged  to  accom- 
modate stresses  by  some  molecular  adjustment  as  well  as  by 
movement  en  masse;  but  accommodation  by  mashing  and  flowage 
differed  at  different  places  and  was  much  more  pronounced  at 
the  east,  in  those  rocks  which  presumably  are  represented  at  the 
west  by  the  blue  limestones  and  their  associated  dolomites  and 
dove-colored  rocks. 

On  the  assumption  that  these  various  calcareous  rocks  just 
mentioned  are  in  general  equivalent  over  wide  areas  and  rest 
on  essentially  the  same  terrigenous  formation  throughout — an 
assumption  that  seems  to  the  writer  to  have  gained  a  consider- 
able degree  of  probability — the  thoughts  arise  as  to  how  this 
relation  came  to  be  established  and  as  to  what  is  the  age  of  the 
terrigenous  rocks.  Some  of  the  latter  have  been  called  Ordo- 
vician  and  some  of  them  Cambrian ;  but  a  field  examination  will 
show  that  it  is  hardly  possible  to  separate  them  as  belonging  to 
different  terranes  on  the  basis  of  the  lithological  features  of  the 
rocks  themselves,  although  certain  types  easily  impress  one  as 
being  of  Cambrian  age  from  a  likeness  to  those  which  have  been 
assumed  with  considerable  positiveness  to  be  Cambrian  and  the 
same  might  be  claimed  for  other  types  with  respect  to  their  in- 
clusion in  the  Ordovician.  Whether  we  call  them  Cambrian  or 
Ordovician,  or  both,  the  problem  remains  of  accounting  for  the 
calcareous  rocks  above  them,  and  the  postulates  which  are  formu- 
lated to  explain  the  present  relations  will  differ  in  the  large  for 
the  different  cases. 

It  was  about  at  this  point  in  the  writer's  studies  that  the 
need  of  certain  more  definite  working  hypotheses  which  could  be 
further  tested  in  the  field  appeared.  Certain  similarities  in  field 
relations  insisted  upon  recognition;  the  terrigenous  rocks,  called 
for  a  more  definite  status  concerning  possible  or  impossible  divi- 
sion and  for  a  more  definite  assignment  as  to  age ;  and  the  ac- 
cumulated evidence  for  the  action  of  powerful  compressive 
stresses  throughout  a  wide  region  and  for  clearly-defined  thrust- 


186  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

ing  in  certain  parts  of  that  region  made  it  necessary  to  ponder  as 
to  the  extent  to  which  thrust  movements  were  involved  in  the 
entire  region's  history. 

The  following  are  examples  of  some  of  the  questions  which 
came  to  mind : 

1.  Is  there  any  evidence  to  show  that  the  calcareous  or  the 
terrigenous  rocks  which  have  been  described  were  first  broken 
and  heaped  up  by  repeated  reverse  faulting  and  then  carried 
westward  as  a  mass  over  other  rocks  along  a  low-angle  thrust 
plane  so  that  they  now  rest  by  thrust  unconformity  on  other 
rocks?  In  this  connection  what  emphasis  is  to  be  put  upon  the 
apparent  present  contact  surfaces  of  the  calcareous  rocks  -  and 
the  terrigenous  formation  on  which  they  rest  or  the  contact 
surfaces  where  the  conditions  are  reversed  and  terrigenous  rocks 
rest  on  limestone? 

2.  Is  there  any  evidence  to  show  that  while  the  calcareous 
rocks  have  been  disturbed  in  position  their  superjacent  relation 
to  the  terrigenous  formation  was  primarily  due  to  normal  marine 
overlap  on  a  floor  of  eroded  older  rocks? 

3.  What  explanation  is  to  be  offered  for  the  apparent  ab- 
sence of  middle  and  later  Cambrian  in  the  general  region  ? 

4.  Is  it  likely  that  the  Beekmantown  as  known  near  the 
lake  is  now  present  at  depth  or  at  the  surface  around  Brandon 
and  in  the  Vermont  valley  or  the  "slate  belt"?  Is  it  likely  that 
it  was  ever  deposited  at  the  east  and  is  there  any  evidence  on  this 
point  ? 

These  questions  and  others  grew  out  of  a  study  of  the  field 
relations  in  western  Vermont  and  the  possible  answers  to  them 
are  part  of  the  problems  of  the  region.  They  will  have  to  be 
considered  again. 

The  "interhedded  series"  of  dolomitic  limestones  and  quartz- 
ites  in  Brandon.  This  series  is  present  in  great  force  in  Brandon 
township,  north,  east  and  south  of  Brandon  village.  In  contrast 
with  the  marble  and  for  the  most  part  with  the  dove-colored 
rock  and  its  associated  gray  or  chamois-colored  dolomite,  the 
bedded  structure  of  this  series  is  well  preserved  in  Brandon, 
in  which  feature  it  resembles  other  exposures  of  the  series  in  the 
Vermont  valley.  The  field  relations  at  Brandon  perhaps  indicate 
its  age  less  decisively  than  at  other  places,  as  at  Bennington,  for 
example ;  but  the  resemblance  of  the  series  to  the  entirely  similar 
rocks  at  Bennington  leaves  no  doubt  of  the  similar  age  of  the  two 
and  little  doubt  of  the  Lower  Cambrian  age  of  the  series. 

In  the  Bennington  region  a  certain  thickness  of  dolomitic 
limestone  intervenes  between  the  quartzite  and  the  interbedded 
series.  In  Brandon  neither  the  quartzite  nor  the  dolomite  are 
in  the  same  simple  relations  to  the  interbedded  series.  In  some 
places  a  dolomite  is  associated  with  the  marble,  as  alluded  to 
above,  and  this  rock  does  not  appear  to  have  the  characters  (3f 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.         ^         187 

the  Striped  rock  that  has  been  described  or  those  of  the  gray  rock 
associated  with  it.  The  dolomite  referred  to  may  be  seen  at 
most  of  the  quarries  around  Brandon  lying  on  or  in  the  marble. 
It  often  separates  the  marble  from  overlying,  interbedded  dolo- 
mites and  quartzites.  As  first  studied  by  the  writer  it  seemed  to 
him  to  be  a  part  of  the  Lower  Cambrian  series,  but  the  field  rela- 
tions are  much  involved  and  not  conclusive  on  this  point.  The 
probability  of  its  inclusion  with  the  Lower  Cambrian  would  seem 
to  depend  to  some  extent  upon  the  interpretation  put  upon  the 
present  structure  of  the  rocks  of  which  it  is  a  part. 

In  a  few  places  members  of  the  interbedded  series  seem  to 
lie  directly  on  the  marble.  Such  relation  was  noted  in  the  field 
just  west  of  the  old  Goodell  quarry  in  Brandon  along  the  old 
stage  road  to  Leicester  and  SaHsbury,  where  stringers  of  quartz- 
ite,  irregularly  disposed  along  the  strike  lie  directly  on  marble. 
In  places  this  quartzite  thins  out  to  nothing  along  the  strike  and 
at  others  widens  out  beyond  any  probable  thickness  of  any  of  the 
quartzite  beds  of  the  series.  These  stringers  look  in  fact  like 
eroded  remnants  of  members  of  the  series  which  lay  in  a  rather 
flattish  position  upon  the  marble.  East  of  the  road  a  few  feet 
of  dolomite  lie  on  the  marble  in  the  old  Goodell  quarry  and  above 
it  is  the  interbedded  series  again.  A  few  rods  west  of  the  expo- 
sures showing  the  quartzite  stringers  is  a  ridge  composed  of  the 
gray  dolomite  and  the  dove-colored  limestone  on  which  no  recog- 
nized traces  of  the  interbedded  series  is  now  present.  Northwest 
of  this  ridge,  across  the  road,  are  outcropping  ledges  of  a  band  of 
marble  which  is  succeeded  westward  by  another  ridge  at  the 
south  end  of  which,  in  the  open  pasture  just  east  of  the  back 
road  to  Morgan's  Stock  Farm,  is  an  abraded  anticline  of  what 
is  interpreted  as  the  interbedded  series.  The  western  limb  de- 
scends across  the  back  road  to  the  plain  of  Otter  Creek.  Traced 
northward  along  the  axis  of  the  fold  the  interbedded  rocks  give 
place  to  the  gray  dolomites  and  associated  dove-colored  rock, 
but  farther  north  on  the  northern  side  of  a  crossroad  appear 
various  eroded  exposures  of  what  appears  to  be  the  dolomite- 
quartzite  interbedded  series.  The  relations  as  thus  described  show 
the  marble  and  its  associated  gray  dolomite  and  limestone  to  be 
overlain  by  an  eroded  mass  of  the  interbedded  dolomites  and 
quartzites  northwest  of  Brandon  village. 

After  an  examination  of  the  rocks  in  Orwell  these  relations 
were  reviewed.  While  the  interbedded  rocks  northwest  of  Bran- 
don bear  some  resemblance  to  members  of  the  Beekmantown 
west  of  Orwell  village,  they  do  not  seem  to  be  sufficiently  like 
them  to  change  the  writer's  earlier  assignment  of  them  to  the 
Lower  Cambrian.  Moreover,  they  showed  no  traces  of  fossils. 
They  have  some  differences  at  places  from  the  interbedded  rocks 
east  of  Brandon  village,  which  seem,  however,  to  be  due  to  a 
shearing  more  nearly  parallel  to  the  bedding.     Rocks  like  those 


188  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

just  described  as  probably  Lower  Cambrian  also  occur  just 
north  of  the  Rutland  R.  R.  track,  and  two  miles  south  an  "island" 
in  the  plain  of  Otter  Creek  shows  these  rocks  prominently  ex- 
posed again  on  precisely  the  same  meridian  as  those  at  the  north, 
and  farther  south,  still  on  the  same  meridian,  northwest  and  west 
of  the  Seager  farm,  they  outcrop  again.  They  may  thus  be 
traced  north  and  south  through  a  distance  of  about  three  miles. 

In  places  at  the  north,  near  the  axis  of  the  fold,  there  is 
pronounced  shearing  structure  developed  across  the  bedding, 
but  at  other  places  along  the  axis  where  the  beds  lie  more  nearly 
flat  and  along  the  slopes  of  the  western  limb  of  the  fold,  shearing 
seems  to  be  more  nearly  with  the  bedding,  producing  thin,  sheeted 
structure,  and  at  many  places  these  thin  sheets  are  distinctly 
crinkled.  Stringers  and  patches  of  salmon-yellow  calcite  mixed 
with  quartz  occur  abundantly  over  the  eroded  exposures  of  these 
thinly-sheared  beds. 

Northeast,  east  and  southeast  of  Brandon  village,  west  of 
the  road  from  Forestdale  to  Pittsford,  the  interbedded  series  is 
disposed  in  regular  and  irregular  folds,  often  closely  compressed, 
frequently  overturned,  and  ruptured  at  many  places  along  the 
strike,  and  probably  also  across  it.  A  rupture  along  the  strike 
may  frequently  be  seen  passing  into  a  fold.  Over  these  parts 
of  the  Brandon  area  the  marble  is  wholly  covered  by  these  inter- 
bedded rocks,  which  are  generally  marked  by  higher  altitude  and 
greater  thickness  than  elsewhere  near  Brandon. 

Some  of  the  ruptures  in  the  series,  just  referred  to,  seem 
clearly  to  be  reverse  faults,  which  are  best  shown  at  those  places 
where  members  of  the  series  stand  on  edge,  or  are  inclined  at 
high  angle  with  easterly  dip,  while  contiguous  members  at  the 
west  dip  at  a  moderate  angle  to  the  westward.  One  of  these 
localities  is  a  mile  east  of  Brandon  village,  at  Cheney  corner.  See 
section,  figure  15. 


Figure  15.  Structure  shown  by  members  of  the  interbedded  dolomites  and 
quartzites  east  of  Brandon  village,  near  Cheney  corner ;  close  folding 
and  reverse  faulting. 

East  of  the  Forestdale-Pittsford  road.       The  interbedded 
series  as  described  for  the  area  east  of  Brandon  village  is  sue- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  189 

ceeded  on  the  east  by  terraced  sand  plains  of  old  delta  deposits 
and  east  of  the  Forestdale-Pittsford  road  by  heavy  bowlder  drift 
which  conceal  outcrops.  The  heavy  drift  forms  the  lower  west- 
ern slopes  of  a  series  of  high,  ridge-like  hills  which  begin  in 
Forestdale  and  extend  southward  through  Coxe,  Mountain  in 
Pittsford.  This  range  of  hills  is  separated  throughout  most  of  its 
length  from  the  steep,  scarped  slopes  of  the  Green  Mountain 
plateau  by  the  valley  of  Sugar  Hollow  Brook. 

The  exposures  in  these  hills  from  Forestdale  southward 
present  many  features  for  comparison  with  the  rocks  forming  the 
Sudbury  and  Orwell  hills  of  the  Taconic  range.  It  is  possible 
to  identify  some  of  the  types  in  these  foothills  of  the  plateau  with 
characteristic  ones  of  the  range.  In  the  eastern  hills  there  occurs 
a  dolomitic  limestone  in  association  with  the  quartzite  and  phyl- 
lite  which  is  now  apparently  wholly  absent  in  the  Taconic  hills 
of  southwestern  Brandon,  Sudbury  and  Orwell,  except  for  some 
doubtful  rocks  on  the  eastern  slope  of  Castle  Mountain  which 
have  been  mentioned. 

Southeast  of  Forestdale  are  ledges  of  massive,  brown  quartz- 
ite which  are  separated  at  the  present  surface  by  a  space  of  nearly 
a  mile  from  the  most  eastern  exposures  of  the  interbedded  series 
east  of  the  village.  Four  miles  to  the  south,  however,  the  inter- 
bedded rocks  are  separated  by  only  one-fourth  of  a  mile  from 
the  drift  slope  of  the  range  of  quartzite  hills.  Southeast  of 
Forestdale,  back  in  the  woods,  is  a  considerable  scarp  and  west 
of  it,  in  the  open  fields  just  outside  the  village,  is  a  succession 
of  smaller  scarps  dropping  off  westward.  West  of  the  second 
of  these  dolomitic  limestone  apparently  rests  on  the  quartzite, 
but  elsewhere  in  the  vicinity  the  dolomite  was  not  seen.  Due 
north  of  these  ledges,  along  their  strike,  on  the  road  to  Goshen, 
just  east  of  Forestdale,  are  ledges  of  black  phyllite  and  quartzitic 
schist  entirely  similar  to  those  seen  in  Sudbury  and  Orwell  and 
also  at  other  places  in  this  eastern  range  that  will  presently  be 
mentioned. 

Going  southeast  .  from  Forestdale,  ledges  of  quartzite  are 
numerous  at  many  places  and  it  is  possible  to  trace  this  rock 
through  the  woods  and  clearings  along  the  low  range  of  hills 
to  Coxe  Mountain.  Exposures  are  chiefly  found  along  the  higher 
western  slopes  and  summits.  There  are  a  number  of  significant 
associations  which  should  be  mentioned. 

The  hill  road  going  east  from  the  Forestdale-Pittsford  road 
about  two  miles  south  of  Forestdale  crosses  the  summit  of  this 
range  of  hills  and  descends  to  Sugar  Hollow.  The  summit  point 
is  known  locally  as  "Birch  Hill." 

On  the  ridge  north  of  Birch  Hill,  massive,  brown  quartzite 
forms  the  higher  part  of  the  western  slope  and  is  in  contact  with 
schist  or  phyllite  which  overlies  the  quartzite  and  extends  east- 
ward and  northward  along  the  ridge.     The  black  phyllite  or  schist 


190  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

forms  large  exposures,  but  is  roughly  intermingled  on  a  large 
scale  with  quartzitic  schist,  or  schistose  quartzite,  in  which  at 
places  are  large,  chunky  veins  of  quartz  which  have  been  opened 
by  zealous  seekers  for  gold.  In  one  of  the  pits  was  noted  a 
black,  graphitic  schist  carrying  pyrite  and  quite  like  that  seen  at 
places  in  Orwell.  The  dip  of  the  rocks,  which  is  probably 
cleavage  structure  in  part,  is  easterly.  The  western  slope  of  the 
ridge  north  of  Birch  Hill  has  scarps  above  the  drift-covered  por- 
tion and  the  eastern  slope  is  abrupt  and  regarded  as  marking  a 
fault  displacement.  No  dolomite  was  found  along  the  top  of  the 
ridge;  but  northeast  of  Churchill's  house  on  Birch  Hill,  on  the 
eastern  slope,  are  small  patches  of  dolomite,  apparently  in  place. 
South  of  Churchill's  house,  across  the  road,  an  east-west  section 
gives  massive  quartzite  at  the  west,  then  eastward  quartzitic  schist 
with  a  small  patch  of  dolomite. 

South  of  Churchill's  house  and  west  of  the  Sugar  Hollow 
road,  patches  of  dolomitic  limestone  occur  sparingly  as  remnants 
of  erosion  on  the  eastern  slope  of  the  ridge.  At  places  also  the 
same  association  of  quartzitic  schist  and  phylhte  with  massive 
quartzite  noted  at  the  north  occurs  along  the  southern  extension 
of  the  ridge.  East  of  an  old  road  which  joins  the  Sugar  Hollow 
road  with  the  Birch  Hill  road,  on  the  east  side  of  a  gulley,  is 
quartzitic  schist  carrying  pyrite  and  overlain  by  dolomite,  while 
west  of  the  gulley  are  big  ledges  of  massive  brown  and  granular 
quartzite  which  continue  on  the  strike  to  join  the  exposures  north 
of  the  Birch  Hill  road. 

South  of  Churchill's  corner  the  Sugar  Hollow  road  descends 
for  a  mile  over  a  gentle  slope  nearly  to  the  brook.  The  old  road 
over  the  ridge  passes  through  a  sort  of  col  which  may  mark  a 
structural  sag,  for  directly  south  of  the  point  where  the  old  road 
joins  the  Hollow  road  the  quartzite  gave  a  reading  of  N.  72°  E. 
and  a  dip  of  36°  N.,  which  is  a  marked  deviation  from  the  prevail- 
ing north-south  strike  of  the  rocks.  Directly  north  of  the  place 
giving  this  anomalous  reading,  dolomite  rests  on  the  quartzitic 
rock  and  its  presence  here  leads  to  a  suspicion  that  the  low  pass 
just  north  may  be  due  to  erosion  of  dolomite  lying  in  an  irregular 
sag. 

Just  south  of  the  point  where  the  old  road  joins  the  Hollow 
road  a  scarp  appears  west  of  the  Hollow  road  and  continues  south- 
ward. 

Two  miles  south  of  Churchill's  corner  a  small  basin  in  the 
hills  holds  Sugar  Hollow  Pond.  The  basin  is  a  faulted  one. 
Scarps  bound  it  on  the  east,  northeast  and  probably  on  the  south. 
East  of  the  pond  is  a  succession  of  low  ridges  broken  by  strike 
faults  which  are  marked  by  westward- facing  scarps  and  inter- 
vening swampy  gullies. 

The  terrigenous  rocks  composing  these  hills  of  the  ridge  or 
range  just  described  present  many  similarities  to  those  west  of 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  191 

Brandon  in  Sudbury,  both  in  their  lithology  and  structure.  They 
are  evidently  broken  by  numerous  faults  as  well.  Massive  quartz- 
ite  is  more  abundant  at  the  east  and  a  dolomite  is  present  at 
places,  but  otherwise  the  student  will  be  impressed  by  the  very 
strong  similarities,  amounting  to  identities  so  far  as  distinguishing 
among  them  is  concerned. 

It  has  been  suggested  above  that  the  terrigenous  rocks  of 
Sudbury  pass  beneath  the  marbles  of  the  Otter  Creek  valley  to 
join  others  at  the  east.  This  should  be  construed  as  only  a 
general  statement;  no  implication  was  intended  that  the  ter- 
rigenous rocks  at  the  east  may  not  have  been  greatly  disturbed 
in  position. 

East  of  Sugar  Hollozv  Brook.  East  of  the  brook  the  to- 
pography is  marked  by  sheer  precipices,  steep  slopes  and  a  rugged 
surface  generally.  Displacements  by  faulting  are  very  evident. 
The  western  scarps  which  were  cleared  by  glacial  action  were 
too  high  and  extensive  to  be  banked  and  covered  with  drift  and 
now  offer  a  somewhat  imposing  view  when  observed  nearby. 

In  common  with  other  portions  of  the  western  edge  of  the 
plateau  the  total  displacement  now  apparent  between  general  up- 
throw and  downthrow  areas  has  often  been  effected  along  several 
distinct  planes.  Along  what  appears  as  a  single  plane  the  amount 
of  displacement  will  vary  at  different  places  along  the  strike. 
A  scarp  will  often  pass  into  a  monoclinal  fold  and  at  some  in- 
definite distance  across  the  strike  will  be  replaced  by  another 
scarp  which  will  perhaps  overlap  the  former  along  the  strike  and 
perhaps  also  another  which  has  in  its  turn  replaced  the  second. 
This  arrangement  impresses  the  observer  of  the  topography  east 
of  Sugar  Hollow  Brook. 

From  the  junction  of  its  head  streams  the  brook  flows  at  the 
base  of  a  prominent  scarp  on  the  west  of  the  Chaffee  Mountain 
mass.  The  considerable  height  of  the  scarp  may  be  seen  very 
clearly  where  a  recent  slide  has  cleared  it  of  trees  and  other  vege- 
tation. This  scarp  is  replaced  eastward  by  another  higher  preci- 
pice at  whose  summit  is  a  shelf  'that  on  a  clear  day  gives  one  of 
the  finest  views  in  the  Vermont  valley. 

Chaffee  is  best  ascended  along  its  northern  slope  from  the 
valley  of  the  eastern  tributary  of  Sugar  Hollow  Brook.  Massive 
quartzite  forms  the  bed  of  this  tributary  and  its  valley  and  the 
ascent  of  Chaffee  is  over  similar  quartzite,  dipping  easterly, 
which  can  be  followed  to  the  shelf  above  mentioned  and  from  the 
latter  place  to  the  summit  where  the  easterly  dip  still  prevails. 

The  ascent  of  Chaffee  was  made,  by  the  writer  under  trying 
conditions ;  the  summit  was  enveloped  in  clouds  and  the  rain 
came  down  in  torrents.  The  atmospheric  conditions  caused 
some  bewilderment  so  that  observations  could  not  be  made  with 
the  desired  accuracy  in  the  thick  woods  of  the  mountain.  About 
a  mile  as  estimated,  south-southeast  of  the  summit  of  Chaffee 


192 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


Mountain,  along  the  upper  portions  and  summit  of  an  eastward 
slope  is  dolomitic  limestone,  which  here  from  the  field  relations 
apparently  lies  on  the  quartzite.  A  sort  of  col  here  permits  an 
easy  descent  on  the  west  side  which  is  made  over  dolomite  and 
quartzite  by  zigzagging  down  slope  among  a  number  of  small 
scarps  to  the  valley  of  Sugar  Hollow  Brook. 

On  a  subsequent  trip  along  the  western  slope  of  the  "Moon- 
shine"-Nickwaket  range,  along  an  old  wood  road  that  ascends  to 
the  col  mentioned  above,  black  phyllite  was  found  in  a  scarp 
overlain  by  massive  quartzite  which  was  succeeded  up  the  slope 
by  exposures  of  dolomite.  There  is  a  small  settlement  on  the 
mountain  side  above  the  contour  of  the  scarp  and  at  the  base  of 
Nickwaket  and  in  the  cleared  fields  of  these  farms  the  dolomite 
is  extensively  exposed.  On  the  east  side  of  a  road  through  the 
settlement,  near  its  northern  termination,  the  dolomite  dips  east- 
ward at  a  moderate  angle,  but  farther  east  up  the  slope  the  dip 
is  westward  at  a  high  angle. 

A  half  mile  southwest,  west  of  this  back  road,  the  surface 
rock  shows  undulating  not  much  compressed  interbedded  dolo- 
mitic and  quartzitic  layers  which  resemble  the  interbedded  series. 
These  are  bordered  by  a  scarp  on  the  west,  at  whose  base  is  a 
black,  sheared  quartzitic  schist,  which  southward  passes  into 
massive  quartzite.  Then  westward  the  dolomite  again  forms  the 
surface  rock  which  farther  south  on  the  slope  and  in  the  valley 
of  the  brook  can  be  seen  grading  downward  into  quartzite  and 
arkose,  all  dipping  easterly  at  a  moderate  angle.  West  of  these 
outcrops  is  Sugar  Hollow  road  and  then  the  quartzite  of  Coxe 
Mountain. 


Figure  16.  A  generalized  surface  section  of  tlie  margin  of  the  Green  Moun- 
tain plateau  southeast  of  Brandon  village,  from  Nickwaket  Mt.  west- 
ward through  Coxe  Mt.  with  offsets  along  the  strike.  Principal  offset 
shown  by  dotted  line.  A,  dolomite;  B,  "interbedded  quartzites  and  dolo- 
mites" ;  C,  quartzitic  schist ;  D,  quartzite  and  arkose ;  E,  quartzite ; 
F,   probable  faults. 

The  observer  passing  northward  along  the  Sugar  Hollow 
road,  from  the  point  where  the  back  road  referred  to  above  joins 
the  Hollow  road,  would  hardly  fail  to  notice  the  conspicuous 


ifM 


o  aj 

55 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  I93 

ledges  of  dolomite  on  the  east  side  of  the  road  and  would  hardly 
fail  to  see  that  the  beds  are  always  folded  and  sometimes  over- 
turned to  the  west.  Throughout  the  same  distance  on  the  west 
side  of  the  road  the  quartzite  of  the  ridge  extending  northward 
from  Coxe  Mountain  is  broken  by  a  scarp  on  the  east.  Some 
dolomite  occurs  on  the  west  side  of  the  road.  The  scarp  ends 
at  the  north  at  the  place  where  the  anomalous  strike  in  the 
quartzite  was  noted.  East  of  the  road  at  this  point  dolomite 
dips  at  a  gentle  angle  easterly,  but  on  the  west  side  of  the  road  it 
shows  much  confusion. 

East  of  Sugar  Hollow  Brook  then  are  found: 

1.  Massive  quartzite  forming  the  prominent  scarps; 

2.  Dolomitic  limestone  at  places  on  the  summits  and  in  large 
exposures  on  the  western  slope  of  this  mountainous  strip,  ap- 
parently resting  on  quartzite; 

3.  Black  phyllite  and  quartzitic  schist  in  scarps  overlain  by 
massive  quartzite ; 

4.  Apparently  some  representatives  of  the  interbedded 
series,  whose  relations  are  not  clear,  but  which  presumably  rest 
on  the  dolomite. 

This  whole  series  has  clearly  undergone  much  disturbance, 
in  fact  more  than  one  deformation,  but  it  seems  reasonably  clear 
that  the  rocks  all  belong  to  one  series  and  that  they  are  of  Lower 
Cambrian  age  by  analogy  with  other  rocks  having  similar  char- 
acters and  relations  in  other  parts  of  the  Vermont  valley.  The 
original  depositional  sequence  is  not  clear  from  the  interrelations 
shown  east  of  Brandon.  From  the  relations  at  Bennington  we 
have: 

1.  Massive  quartzite,  at  the  base; 

2.  Dolomitic  limestone ; 

3.  Interbedded  series. 

The  relation  of  the  schist  is  not  wholly  clear.  It  seemed  to 
be  a  part  of  the  basal  quartzite  formation  and  interstratified  with 
it.  In  explaining  the  present  field  relations,  account  must  be 
taken  of  erosion  as  well  as  deformation. 

General  structural  relations  of  the  interbedded  series  and  the 
rocks  of  the  plateau  east  of  Brandon.  The  interbedded  series 
just  east  of  Brandon  clearly  shows  within  itself  deformational 
features  of  several  kinds,  most  of  which  are  due  to  compression 
and  some  of  which  are  the  result  of  normal  faulting.  The  effects 
of  compression  may  be  summarized  as  follows:  (a)  buckling, 
with  frequent  formation  of  tightly  compressed  folds,  which  are 
often  overturned;  (b)  shearing  across  the  bedding  of  the  folds; 
(c)  reverse  faulting  along  the  strike,  which  is  indicated  clearly 
at  several  places. 

The  field  relations  which  the  interbedded  series  has  to  the 
other  strata  with  which  it  is  now  associated  around  Brandon 
village,  in  the  writer's  opinion,  could  leave  little  doubt,  after  a 


J94  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

careful  field  inspection,  that  the  former  is  superjacent  to  the 
marble  and  the  dove-colored  limestone  and  its  gray  dolomite 
associate.  The  interbedded  series  has  been  worn  through  over 
many  large  and  small  areas,  with  the  consequent  exposure  of  the 
other  rocks  on  which  it  lay.  The  more  or  less  detached  exposures 
of  the  interbedded  rocks  along  its  western  portion  west  of  Bran- 
don are  inliers  of  this  formation  on  presumably  younger  rocks, 
or  are  in  process  of  becoming  such.  This  relation  makes  the 
marbles  and  their  associated  rocks  outlying  belts  in  an  older  series. 
The  number  of  contacts  and  outcrops  that  reveal  this  relation  is 
manifestly  reduced  by  concealment  under  drift  or  by  difficulty  of 
correlation  of  certain  dolomites  lying  on  the  marble.  There  may 
also  have  been  some  deformation  of  all  these  various  rocks,  in- 
cluding their  plane  of  contact,  subsequent  to  that  which  super- 
posed the  older  series  on  the  younger  strata.  The  evidence  may 
be  summarized  as  follows : 

1.  The  contrast  in  metamorphism  and  deformational  fea- 
tures which  the  two  formations  show  when  in  proximity ; 

2.  Ragged  erosional  remnants  of  the  resistant  quartzitic 
members  of  the  interbedded  series  on  the  marble  and  its  associated 
rocks  at  various  places ; 

3.  The  interrupted  outcroppings  in  bands  of  the  marble 
through  the  interbedded  series  and  a  probably  related  dolomite. 

From  the  east- west  width  of  the  area  in  which  the  marble 
outcrops  through  the  interbedded  formation  we  may  infer  with 
some  reason  that  the  marble  underlies  the  interbedded  rocks  east 
of  Brandon ;  but  how  much  farther  east  the  marble  extends  at 
depth  is  a  question  whose  answer  would  depend  a  good  deal  on 
the  interpretation  given  to  the  relations  of  the  rocks  of  the  plateau 
to  those  of  the  valley. 

There  is  little  hint  of  what  lies  at  depth  beneath  the  sand 
plains  and  drift  that  occupy  the  space  of  varying  width  along  the 
Forestdale-Pittsford  road  between  the  interbedded  series  and  the 
range  of  quartzite  hills  east  of  the  road.  Farther  north,  east  of 
Lake  Dunmore,  a  prominent  scarp  marks  a  normal  fault  and  this 
scarp  falls  precisely  along  the  line  of  the  projection  of  the  Forest- 
dale-Pittsford road  northward.  The  great  pile  of  drift  that 
extends  along  the  western  slope  of  the  ridge  south  of  Forestdale 
suggests  that  a  cliff  has  afford'ed  a  convenient  place  in  which  to 
pile  this  debris.  The  slighter  development  of  drift  at  the  north 
around  Dunmore,  in  contrast  with  conditions  east  of  Brandon,  is 
quite  in  consonance  with  the  variability  in  this  respect  shown  by 
other  portions  of  the  Vermont  valley.  It  is  close  to  the  line  of 
this  assumed  displacement  east  of  Brandon  that  the  kaolin  mine 
at  Forestdale  with  its  deposits  of  lignite  and  limonite  occurs. 

Prominent  scarps  bound  the  interbedded  series  on  the  east, 
southeast  of  Brandon  village,  west  of  the  Pittsford  road.  Their 
significance    is    not    clear.      They    suggest    displacements.     Pre- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  195 

glacial  and  base-levelling  forces  and  glacial  plucking,  evidently- 
availed  themselves  of  a  general  line  of  crustal  weakness  along  the 
region  of  the  intervening  surface  space  just  described.  The  map 
brings  the  interbedded  series  and  quartzite  in  contiguity;  but  the 
implication  is  general  rather  than  precise,  for  there  are  indica- 
tions at  Forestdale  that  schist  or  phyllite  lies  beneath  quartzite 
and  it  is  not  unreasonable  to  think  that  the  presence  of  more 
friable  schist,  interbedded  with  the  quartzite,  might  have  been  the 
primary  contributing  cause  of  the  space  that  has  been  mentioned. 

The  quartzite  of  the  ridge  south  of  Forestdale,  which  is 
overlain  and  possibly  underlain  by  phyllite  and  therefore  inter- 
bedded with  it,  joins  at  the  present  surface  with  the  quartzite  of 
the  higher  plateau  slopes  east  of  Forestdale  which  affords  some 
reason  for  regarding  them  of  the  same  age  and  therefore  for 
regarding  the  terrigenous  rocks  of  the  Orwell  and  Sudbury  hills 
as  in  part  of  the  same  age  as  the  plateau  rocks.  But  it  seems 
that  too  much  reliability  should  not  be  placed  upon  the  present 
surface  continuity  alone,  here  or  elsewhere  in  the  Vermont  val- 
ley, in  view  of  unquestionable  deformation  of  more  than  one  kind 
and  the  probability  of  lateral  as  well  as  vertical  displacement  of 
the  rocks  now  forming  the  edge  of  the  plateau. 

It  is  not  easy  to  fix  the  precise  relation  of  the  schist  in  the 
ridge  south  of  Forestdale  to  the  associated  quartzite  by  reference 
to  these  rocks  alone.  It  appears  to  be  conformable.  It  is  even 
harder  to  be  satisfied  of  the  relation  which  the  patches  of  dolo- 
mite along  this  ridge  have  to  the  schist  and  quartzite.  It  seems 
rather  likely  that  the  formation  which  forms  the  probable  basal 
member  of  this  series  of  quartzite  and  phyllites,  dolomites,  etc., 
as  a  depositional  mass  varied  originally  in  composition,  both  later- 
ally and  vertically,  not  only  as  a  result  of  overlap,  but  from  other 
causes  as  well  and  that  a  vast  mass  of  sands  and  muds  of  dif- 
ferent kinds  was  finally  spread  over  the  sea  floor. 

In  general  it  would  appear  that  the  quartzite-phyllite  forma- 
tion is  basal  to  the  dolomite  and  that  the  former  has  been  elevated 
against  the  interbedded  series  by  reverse  faulting  and  that  a 
lateral  thrust  has  carried  the  latter  over  the  marble  and  its  asso- 
ciated rocks  at  the  west.  It  does  not  seem  possible  to  account  for 
the  present  superposition  of  the  interbedded  series  on  the  marble 
and  its  associated  rocks  on  any  other  basis,  if  the  conclusions 
regarding  the  relative  ages  of  these  formations  are  in  general 
correct.  Apparently  the  lateral  thrust  drove  for  some  distance 
above  the  schist  and  through  the  dolomite,  for  the  schist  appears 
nowhere  in  the  Brandon  region  between  the  marble  and  the 
interbedded  series,  although  it  is  entirely  possible  that  the  marble 
extends  at  depth  beneath  the  quartzite-schist  ridge  east  of  the 
Forestdale-Pittsford   road. 

It  seems  reasonably  clear  that  the  interbedded  series  and  the 
quartzite-phyllite  formation  belong  to  one  terrane  from  the  rela- 


196  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

tions  which  they  have  to  each  other  throughout  the  Vermont 
valley.  If  the  interbedded  series  has  been  thrust  on  younger 
rocks  we  may  reasonably  infer  that  probably  the  quartzite  has 
also.  The  field  relations  of  the  interbedded  series  give  the  clue 
to  the  meaning  of  the  position  of  the  quartzite  and  schist  east 
of  it ;  the  latter  have  been  brought  up  by  reverse  faulting  as  the 
result  of  rupture  following  compression  and  probably  a  low  angle 
thrust  plane  cuts  the  reverse  fault  plane  somewhere  at  depth.  It 
is  not  so  apparent  whether  the  quartzite  with  its  overlying  dolo- 
mite east  of  Sugar  Hollow  Brook,  which  now  form  the  rugged 
edge  of  the  plateau,  are  separated  by  a  reverse  fault  from  the 
quartzite-phyllite  west  of  the  brook,  because  normal  faulting  ob- 
scures the  relations  between  the  two ;  but  while  the  peculiar 
pattern  of  these  normal  displacements,  in  which  the  faults  pass  at 
the  present  surface  into  folds,  suggests  that  except  for  normal 
faulting  these  various  terrigenous  rocks  east  of  the  interbedded 
series  are  not  broken  except  by  tension  faults  within  the  area  of 
the  map,  conditions  at  other  places  may  lead  to  another  conclu- 
sion. 

Approaching  the  question  of  the  correlation  of  the  terrige- 
nous rocks  on  the  west  and  east  of  Sugar  Hollow  Brook  from 
the  viewpoint  of  their  general  associations,  their  similarity  in  age 
and  common  membership  in  the  basal  formation  gains  consider- 
able increase  in  probability,  in  the  writer's  opinion.  So  far  as 
the  writer's  observations  go  there  is  no  reason  to  suppose  that  the 
quartzite  of  Chaffee  Mountain,  "Moonshine"  and  Nickwaket, 
and  certain  quartzites  and  arkoses  in  the  valley  of  Sugar  Hollow 
Brook  are  any  older  than  the  quartzites  and  phyllites  of  the  ridge 
of  hills  west  of  the  brook.  The  rocks  west  of  the  brook  are 
dismembered  portions  of  the  plateau,  dropped  down  by  faulting, 
in  the  formation  of  a  great  downthrow  region.  In  this  down- 
thrown  mass  the  interbedded  series,  of  course,  also  belong. 

How  far  east  the  marble  may  extend  beneath  the  rocks  of 
the  plateau  is  a  question  whose  answer  rests  wholly  upon  the 
answer  to  the  prior  question  of  how  Jar  does  the  thrust  plane, 
whose  existence  seems  to  be  established  by  the  present  relations 
of  the  interbedded  series,  extend  east  of  the  present  western  edge 
of  the  plateau.  If  the  thrust  arose  in  a  reverse  fault  near  the 
present  margin,  then  presumably  on  the  basis  of  the  relations 
which  the  marble  seems  to  have  to  these  terrigenous  rocks  and 
the  equivalence  of  the  latter  to  each  other,  the  marble  would  not 
be  found  at  depth  east  of  such  a  root  fault.  The  thrust  plane 
cannot  be  traced  eastward  beyond  the  exposures  of  the  marble 
and  its  associated  rocks  from  beneath  the  interbedded  series 
because  its  trace  must  be  made  from  the  surface.  There  does 
not  appear  to  be  visible  at  the  present  surface  any  transection  of 
the  plane.  Reconnaissance  trips  by  the  writer  in  the  plateau 
have  failed  thus  far  to  give  anything  that  could  be  construed  as 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  I97 

the  root  of  a  great  thrust.  Its  eastward  extension  is  wholly 
problematical. 

It  was  suggested  above  that  probably  a  lateral  thrust  in  car- 
rying the  interbedded  rocks  over  on  the  marble  had  sheared 
above  the  basal  formation  into  the  calcareous  members  of  the 
Lower  Cambrian  rocks.  An  important  principle  seems  to  be 
involved  here.  Probably  we  are  inclined  to  look  for  too  much 
regularity  in  the  manner  in  which  a  great  lateral  thrust  would 
drive  through  a  mass  of  rocks.  Because  the  thrust  has  apparently 
cut  in  a  certain  way  through  the  rocks  now  near  Brandon  is  no 
positive  indication  that  the  shear  would  have  been  just  like  it  at 
other  places,  while  the  general  fact  of  an  elevation  of  Lower 
Cambrian  rocks  and  overthrusting  by  them  would  still  hold  for 
many  places.  In  other  words,  we  might  expect  that  in  some 
cases  the  plane  of  thrust  would  have  been  such  as  to  carry  the 
terrigenous  rocks  of  the  east  over  on  the  marble  and  its  asso- 
ciated rocks.  The  recognition  of  such  a  possibility  in  the  pres- 
ence of  evidence  for  general  overthrusting  might  greatly  affect 
the  interpretation  of  relations  at  many  places  and  such  possibility 
will  be  called  to  mind  in  dealing  with  certain  relations  farther 
south  in  the  Vermont  valley. 

In  considering  the  ideas  and  possibilities  which  have  just 
been  discussed,  the  question  continually  arises  in  one's  mind  as 
to  what  extent  these  various  rocks  were  covered  by  others  at  the 
time  of  overthrusting.  Did  the  overriding  Cambrian  carry  with 
it  a  heavy  load  of  younger  rocks  ?  Certain  other  questions  arise : 
Did  the  marbles  which  are  now  found  west  of  the  plateau  once 
extend  over  it  to  the  eastward?  Is  there  more  than  one  thrust 
plane,  one  by  which  the  marble  and  its  apparent  counterparts 
at  the  west,  together  with  their  associated  rocks,  were  heaped  up 
and  carried  westward  and  another  along  which  the  Lower  Cam- 
brian rocks  broke  through  the  marbles  and  overrode  them?  Did 
the  latter  rupture  occur  first  and  so  bring  an  extra  load  on  the 
calcareous  rocks  now  represented  by  the  marble  and  thus  cause 
their  greater  metamorphism  ?  Were  the  marbles  and  their  counter- 
parts ever  covered  with  other  rocks,  especially  with  terrigenous 
rocks?  They  have  been  assumed  to  have  been  and  the  marble 
has  been  assumed  to  have  been  thrust  through  the  younger  ter- 
rigenous rocks  or  exposed  on  anticlinal  folds  through  them. 
Why  do  not  terrigenous  rocks  appear  between  the  marbles  and 
the  interbedded  series  around  Brandon,  not  by  overthrust  of 
lower  members  of  the  Cambrian,  but  because  the  marbles  were 
overlain  by  terrigenous  rocks?  Is  it  because  these  were  eroded 
before  the  thrust  of  the  Lower  Cambrian?  Was  the  thrust 
which  we  now  see  evidence  of  around  Brandon  an  erosion  thrust, 
that  is,  one  consequent  upon  previous  erosion  of  the  various 
rocks?  If  the  terrigenous  rocks  that  are  found  at  places  lying 
above  the  marble  and  which  have  been  described  as  Ordovician 


198  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

are  such,  why  do  not  similar  rocks  appear  above  the  less  meta- 
morphosed Chazy-Trenton  rocks  that  have  been  described  by  the 
writer  on  previous  pages?  Why  are  such  rocks  absent  north  of 
the  Taconic  range  in  Leicester,  Salisbury,  Shoreham  and  neigh- 
boring towns?  Must  we  discount  or  discard  the  ideas  that  the 
various  calcareous  rocks,  which  were  described  as  lying  on  a 
terrigenous  foundation  common  to  all,  are  actually  in  such  relation 
and  essentially  equivalent?  Again  in  this  connection  what  sig- 
nificance has  the  similarity  of  the  terrigenous  rocks  east  of  Bran- 
don to  those  of  the  Sudbury  and  Orwell  hills?  If  some  of  the 
latter  are  of  different  general  age  than  others,  why  does  not 
some  pronounced  structural  arrangement  appear  among  them  so 
that  they  may  be  separated?  If  it  should  prove  more  than 
probable  that  rocks  carrying  fossils  in  Sudbury  have  been  crushed 
into  marble  in  Brandon  does  it  appear  probable  that  difference  in 
degree  of  metamorphism  among  the  terrigenous  rocks  is  any  sure 
criterion  of  difference  in  age?  Is  there  anything  in  the  lithology 
of  the  various  terrigenous  rocks  that  is  positive  enough  to  separate 
them  into  different  terranes?  Has  account  been  taken  of  pos- 
sible overthrust  bringing  schists  into  contiguity  with  less  meta- 
morphosed terrigenous  rocks ;  or  of  an  overthrust  margin  sepa- 
rating rocks  of  one  age  from  those  of  another  on  each  side 
of  it,  except  possibly  where  rocks  which  have  been  overridden 
now  appear  through  the  overthrust  mass  on  account  of  erosion? 
In  a  region  of  thrust  displacements,  how  much  value  can  be  as- 
signed to  apparent  surface  transition?  What  relations  have  the 
overthrust  phenomena  along  the  lake  to  those  at  the  east?  Are 
there  field  relations  anywhere  in  western  Vermont  that  show 
the  Ordovician  rocks  resting  or  probably  resting  on  Lower  Cam- 
brian strata? 

Allusion  has  been  made  to  the  presence  of  a  great  downthrow 
region  bordering  the  Green  Mountain  plateau  for  a  long  distance 
on  the  west.  In  the  writer's  judgment  recognition  of  the  reality 
of  this  great  structural  feature  is  all-important  and  it  seems  to 
him  that  failure  truly  to  appreciate  the  extent  of  the  region  and 
the  significance  of  the  principle  involved  has  been  an  element 
of  confusion  in  his  own  thinking  and  that  of  others. 

At  the  present  time  the  Green  Mountain  plateau  structurally 
appears  to  stand  as  a  great  upthrow  block  of  the  crust  with 
reference  to  certain  rocks  that  lie  to  the  west  of  it.  This  relation 
holds  irrespective  of  whether  the  plateau  has  been  thrust  up  or 
the  other  area  has  sunk;  but  enough  has  probably  been  said  al- 
ready to  show  that  it  is  the  writer's  idea  that  this  present  manifest 
relation  of  upthrow  and  downthrow  regions  was  produced  by 
a  deformation  quite  separate  from  any  of  the  great  overthrusts 
which  have  been  described.  It  is  necessary  to  appreciate  that 
the  genesis  of  this  relation  is  of  much  more  ancient  date  than 
any  purely  physiographic  relations  that  now  obtain  between  the 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  199 

two,  and  that  although  crustal  warping  and  other  disturbances 
may  have  caused  minor  movements  and  changes  in  their  relations, 
in  a  primary  and  larger  sense  the  present  general  relation  of 
upthrow  and  downthrow  areas  probably  antedates  the  destruc- 
tion by  erosion  of  a  loftier  region,  although  one  cannot  be  so 
positive  about  how  long  after  the  great  thrust  movements  of  the 
general  region  the  relation  of  upthrow  to  downthrow  by  normal 
faulting  was  produced,  because  the  date  of  the  thrusts  is  so 
uncertain. 

The  part  of  Vermont  lying  west  of  the  Green  Mountain 
plateau  includes  the  other  physiographic  divisions  described  in 
a  preceding  section  of  this  paper.  From  consideration  of  the 
ways  in  which  rock  deformation  is  known  to  have  occurred  it 
will  appear  that  there  are  several  purely  theoretical  possibilities 
as  to  the  relations  which  the  rocks  of  these  divisions  might  hold 
to  one  another. 

1.  The  Taconic  range,  Vermont  valley  and  Champlain  low- 
land might  all  be  interpreted  as  parts  of  a  general  downfolded 
region  with  respect  to  the  Green  Mountain  plateau  and  as  owing 
their  present  physiographic  contrasts  entirely  to  differential  ero- 
sion of  a  region  of  relatively  simple  folds,  in  which  region  the 
rocks  west  of  the  plateau  constituted  a  compound,  structural 
synclinorium  and  those  of  the  plateau  the  complemental  anti- 
clinorium.  Faulting  and  particularly  thrusting  played  only  minor 
parts  at  any  time  in  the  history  of  the  region.  In  connection  with 
this  view  the  rocks  at  the  west  might  be  considered  as  originally 
members  of  a  great  geosynclinal  of  deposition,  while  those  of  the 
plateau  belonged  largely  to  a  contemporaneous  positive  segment 
of  the  crust.  Sedimentation  might  have  been  interrupted  with- 
out changing  the  essential  relations  of  these  two  regions,  but 
eventually  produced  a  great  thickness  of  rocks  which  were  later 
compressed  without  being  profoundly  displaced  with  respect  to 
one  another. 

2.  The  rocks  lying  west  of  the  plateau  might  all  be  regarded 
as  parts  of  a  great  downfolded  region  without  having  suffered 
much  deformation  by  thrusting,  as  postulated  under  1.  At  some 
subsequent  time  great  trough  faults  were  formed  producing  the 
structural  outlines  of  what  are  now  the  Vermont  valley  and 
Champlain  lowland,  which  stand  as  downthrow  regions  with 
respect  to  both  the  plateau  and  the  Taconic  range.  The  present 
physiographic  relations  are  thus  primarily  structural  in  thei'r 
genesis  and  secondarily  due  to  erosion.  The  rocks  of  the  Taconic 
range  and  the  plateau  have  the  same  general  relations  to  each 
other  that  they  had  originally  and  prior  to  normal  faulting,  except 
for  folding. 

3.  On  the  basis  of  known  overlap  at  certain  places  in  west- 
ern Vermont  of  older  on  younger  strata  the  rocks  at  many  other 
places  within  the  region  might  be  considered  as  now  remote  from 


200  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

their  original  places  of  deposition  as  the  result  of  deformation 
of  the  crust  by  great  thrust  movements  carrying  the  masses  of 
one  segment  of  the  crust  over  on  those  of  another  for  con- 
siderable but  indeterminate  distances,  with  or  without  much  fold- 
ing, thus  bringing  into  juxtaposition  rocks  of  widely  different 
ages.  At  some  time  subsequent  to  such  deformation  by  thrust- 
ing, normal  faulting  occurred  and  produced  the  structural  out- 
lines of  the  Vermont  valley  and  Champlain  lowland.  These 
faults  literally  chopped  these  overthrust  masses  along  many  planes 
and  introduced  a  confusion  calculated  to  baffle  any  attempt  to 
explain  the  present  structural  relations.  If  in  addition  to  these 
deformations  there  were  others,  such  as  folding  of  irregular  thrust 
planes  and  repeated  normal  faulting  a  very  tangled  aspect  would 
undoubtedly  be  produced.  Normal  faulting  in  laterally  thrusted 
masses  conceivably  might  give  relations  that  would  have  strong 
resemblance  to  such  as  would  be  produced  by  reverse  faulting. 

EUTLAND  COUNTY. 

Townships  of  Danby,  Mount  Tabor,  Wallingford,  Tinmouth,  Clarendon, 
Rutland,  Proctor  and  Pittsford. 

(Pawlet,  Wallingford,  Castleton  and  Rutland  topographic  sheets.) 

Topography.  The  areas  which  will  be  described  in  the  town- 
ships mentioned  in  the  heading  for  the  most  part  lie  in  the  Ver- 
mont valley  in  its  extension  north  of  Dorset  Mountain.  The 
rocks  along  the  edge  of  the  Green  Mountain  plateau  at  the  east 
and  a  few  in  the  Taconic  range  will  be  briefly  mentioned. 

The  Vermont  valley  north  of  Dorset  Mountain  is  marked  by 
a  ridge  which  extends  northward  from  Danby  to  Rutland.  The 
place  of  this  ridge  is  then  taken  by  two  shorter  ones;  one  of 
these  separates  the  valley  north  of  Center  Rutland  from  that 
at  West  Rutland  and  the  other  forms  Pine  Hill  northwest  of 
Rutland. 

Otter  Creek  enters  Danby  from  Dorset  at  the  south  and  flows 
in  a  valley  between  the  edge  of  the  plateau  and  the  ridge  that 
runs  north  from  Danby;  but  at  Rutland  the  stream  turns  west- 
ward to  Center  Rutland  and  flows  in  the  Center  Rutland  valley 
west  of  Pine  Hill  as  far  as  Proctor,  where  it  enters  the  wide 
v.alley  in  Pittsford. 

By  the  ridges  mentioned  the  main  valley  is  thus  broken  into 
several  minor  ones  which  have  been  excavated  in  softer  rocks 
than  those  which  compose  the  ridges.  The  surface  topography 
of  this  portion  of  the  Vermont  valley  therefore  differs  from  that 
south  of  Dorset  Mountain,  but  the  main  outlines  of  the  valley 
between  the  plateau  and  the  Taconic  range  are  maintained 
throughout,  except  for  the  interruption  by  the  Dorset  Mountain 
mass. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


201 


General  note.  North  of  Dorset  Mountain  the  Vermont  val- 
ley in  its  extent  from  .Danby  to  Pittsf ord,  including  the  detached 
ridges  that  have  been  mentioned  in  the  brief  discussion  of  the 
topography,  presents  a  great  number  of  most  remarkable  and 
illuminating  field  relations  that  can  be  truly  appreciated  only 
after  an  examination  of  them.  An  adequate  discussion  of  the 
geology  of  this  part  of  the  valley  would  speedily  pass  beyond  the 
limits,  of  a  general  paper  like  the  present  one.  All  that  can  be 
done  is  to  give  what  appears  to  be  essential.  Outside  the  Ben- 
nington and  Brandon  areas  the  writer  spent  more  time  in  this 
than  in  any  other  part  of  the  valley  and  devoted  parts  of  five 
days  to  a  careful  inspection  of  the  region. 

General  description.  North  of  Dorset  Mountain  lies  Danby 
Hill  which,  as  will  be  discussed,  is  separated  by  an  east-west  fault 
at  the  south  from  the  mass  of  Dorset  Mountain  and  which  north- 
ward joins  the  ridge  which  extends  through  Tinmouth,  WaUing- 
ford  and  Clarendon  to  Rutland. 


Figure  17.  Composite  drawing  designed  to  show  structure  of  quartzite  at 
the  foot  of  the  plateau  between  Danby  and  South  Wallingford  and  that 
along  eastern  slope  of  the  Danby-Clarendon  intermediate  ridge  ;  also  that 
of  the  overlying  dolomite.     The  overturning  is  westward. 

On  the  east,  Danby  Hill  slopes  rather  gradually  to  the  plain 
of  Otter  Creek.  North  of  Danby  Hill  the  eastern  slope  of  the 
ridge  is  often  much  sharper  and  sometimes,  near  the  base,  abrupt. 

Danby  Borough  is  on  the  eastern  edge  of  Danby  township. 
Danby  station  is  in.  the  adjoining  township  of  Mount  Tabor.  A 
mile  and  a  fourth  east  of  the  station  begins  the  steep  slope  of 
the  plateau  which  is  cut  east  of  Danby  by  the  gorge  of  the  "Big 
Branch."  In  the  bed  of  this  stream  at  Mount  Tabor  village  the 
compact,  massive  quartzite  outcrops.  Thence  it  may  be  followed 
in  the  valley  northward  to  large  ledges  along  the  railroad  track 
three  miles  north  of  Danby  station.  The  boundary  of  the  quartz- 
ite then  bends  easterly  away  from  the  track  at  South  Wallingford 
and  its  place  is  taken  here  along  the  meridian  of  the  ledges  farther 
south  by  members  of  the  interbedded  series  and  by  limited  out- 
crops of  marble.  The  ledges  of  quartzite  along  the  track  are  only 
a  little  over  a  mile,  if  that,  east  of  quartzite-phyllite  outcrops  on 
the  northeastern  slope  of  Danby  Hill.  Except  for  difference  of 
present  altitude  of  Danby  Hill  and  the  erosion  of  its  eastern 
slope,  the  relations  of  plateau,  narrow  valley,  and  western  ridge 


202  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

at  some  places  in  Danby  is  like  that  farther  south,  east  of  Dorset 
Mountain. 

The  structure  in  the  quartzite  of  the  ledges  along  the  track, 
just  referred  to,  is  generalized  in  the  accompanying  sketch.  See 
figure  17.  A  mile  west  of  these  ledges,  on  the  west  side  of  the 
creek  at  a  sharp  turn  in  the  main  road,  dolomite  shows  the  same 
structure.  We  see  the  quartzite  and  the  superjacent  calcareous 
beds  buckling  under  compression  to  form  overturned  folds. 

The  marble  outcrops  on  the  northeastern  and  northern  flanks 
of  Dorset  Mountain  give  place  northward  under  drift  to  quartzite 
and  to  members  of  the  interbedded  series  of  the  Lower  Cambrian 
in  Danby  Borough  and  along  the  eastern  slopes  of  Danby  Hill. 
In  the  bed  and  banks  of  Mill  Brook  in  Danby  Borough,  beds  of 
dolomite  have  a  flattish  position  with  very  gentle  arching,  slight 
easterly  dip  and  apparently  a  slight  southerly  pitch.  A  mile  and 
one-fourth  southwest  of  these  outcrops  along  the  brook  road 
from  Danby  Borough  to  Danby  Four  Corners,  at  the  bend  in  the 
road,  what  appear  to  be  dolomitic  members  of  the  interbedded 
series  have  been  folded  into  a  small  anticHne  and  overturned  so 
as  now  to  form  an  acute,  recumbent  fold.  East  and  west  of  the 
dolomite  is  quartzite.  Along  the  meridian  of  these  outcrops 
about  one  and  a  half  miles  north  of  them  on  the  eastern  slope  of 
Danby  Hill  the  interbedded  members  of  the  Lower  Cambrian 
series  outcrop  and  here  apparently  mark  the  eroded  edge  of  a 
more  extensive  covering  of  these  rocks.  On  Danby  Hill  they 
extend  eastward  to  join  those  in  the  valley  of  Otter  Creek. 
Further  discussion  of  them  may  be  given  after  following  the 
section  as  begun  along  the  brook  road  and  after  noting  certain 
other  exposures  lying  north  and  south  of  the  road. 

Westward  along  the  brook  road  the  outcrops  of  quartzite 
west  of  the  recumbent  dolomite  give  place  to  a  black  schist,  well 
exposed  in  the  bank  at  the  second  fork  in  the  road  and  which 
continues  northward  over  the  top  of  the  hill  along  the  same  meri- 
dian and  joins  the  schist  exposures  along  the  higher  eastern 
slopes  of  Danby  Hill.  West  of  the  schist  outcrops  in  the  bank 
of  the  road  in  both  of  the  high  walls  of  the  gorge  of  the  brook 
is  somewhat  massive  quartzite.  This  quartzite  was  not  carefully 
traced  northward  at  the  surface,  but  on  the  meridian  of  this 
quartzite  in  the  gorge  of  the  brook,  on  the  southern  slope  of 
Danby  Hills,  occurs  the  black  schist  or  phyllite,  and  the  latter 
occurs  westward  along  the  road  to  Danby  Four  Corners.  South- 
ward towards  Dorset  Mountain  along  a  back  road  are  fine  ex- 
posures of  massive,  brown  quartzite  which  are  surrounded  by 
drift  and  whose  actual  extension  could  not  be  followed.  A  mile 
west  of  these  outcrops  the  bed  of  Mill  Brook,  which  flows  east- 
ward, is  strewn  with  quartzite  boulders.  Hosts  of  big  quartzite 
boulders  fill  the  drift  south  of  Danby  Hill,  which  is  a  feature 
doubtless  associated  with  the  action  of  the  ice  in  stripping  the 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.        '  203 

slopes  and  summit  of  the  hill  and  parts  of  the  ridge  at  the  north. 

One-third  of  a  mile  south  of  Danby  Four  Corners  and  east  of 
the  hamlet  on  the  southwestern  slopes  and  northward  along  the 
lower  western  slopes  of  Danby  Hill  is  a  bluish-gray  or  bluish 
limestone,  weathering  gray  and  appearing  in  many  outcrops. 
Fossils  were  not  found  in  this  rock  by  the  writer,  but  they  have 
been  reported  by  Foerste,^  and  regarded  by  him  as  having  a 
Trenton  aspect.  A  mile  and  a  half  north  of  the  Corners  a  crys- 
talline limestone  shows  a  brecciated  condition  on  the  gray,  weath- 
ered surface,  but  is  quite  healed  and  without  obvious  fragmenta- 
tion on  the  fresh  surface,  which  is  of  dark  blue  color.  From 
t;he  writer's  acquaintance  with  other  areas  this  blue  rock  would 
have  been  tentatively  correlated  with  Trenton  and  certainly  not 
with  the  Cambrian. 

Above  the  blue  limestone  outcrops  at  the  base  of  Danby  Hill, 
along  the  path  up  the  hill  traversed  by  the  writer,  outcrops  are 
lacking  until  about  half  way  up  when  black  phyllite  or  schist 
appears  which  continues  over  the  summit  and  outcrops  at  intervals 
therefrom  down  to  about  the  1,100  feet  contour,  when  the  topog- 
raphy changes  somewhat  in  passing  from  the  schist  to  some  out- 
crops of  sheared,  bluish  marble  standing  on  end  and  then  a  short 
distance  eastward  appears  the  characteristic  association  of  the  jn- 
terbedded  series  of  the  Cambrian,  which  is  traceable  south  by  west 
as  the  eroded  edge  of  the  Lower  Cambrian  series  along  the  slope 
of  Danby  Hill  alluded  to  above.  Some  conspicuous  ledges  of 
massive  quartzite  also  standing  on  end  appear  just  west  of  the 
margin  of  the  interbedded  rocks.  The  surface  succession  is  thus 
within  a  fourth  of  a  mile  or  less  across  the  strike  from  west  to 
east,  with  slight  offsets  to  include  outcrops:  1,  schist;  2,  sheared, 
blue  marble;  3,  massive  quartzite;  4,  interbedded  series. 

A  half  mile  north  of  the  exposures  just  described  the  schist 
outcrops  east  of  the  marble.  There  is,  in  fact,  at  this  place  a 
confusing  intermingling  at  the  present  surface  of  marble,  schist 
and  quartzite. 

North  of  these  ledges,  bearing  to  the  west  across  Baker 
Brook,  the  schist  or  phyllite  forms  most  of  the  surface  outcrops, 
with  occasional  patches  of  limestone  or  marble,  to  the  summit  of 
Clark  Mountain.  Here  on  the  summit  and  western  slopes  mas- 
sive, heavy  quartzite  forms  a  continuous  outcrop  over  large  areas 
with  the  phyllite  or  schist  lying  to  the  east.  Thick  quartzite  dip- 
ping about  30°  westerly  was  traced  for  a  rnile  along  an  old  lumber 
railroad  at  the  summit  of  the  western  slope.  The  western  surface 
slope  of  the  mountain  is  fairly  steep  and  bevels  across  the  west- 
erly dipping  quartzite.  Across  the  road  at  the  western  base  of 
the  mountain  the  interbedded  members  of  the  Cambrian  were 
noted  dipping  66°  westerly  along  a  strike  of  N.  19°  E. 

lAmer.  Jour.  Sci.,  1893,  vol.  46,  pp.  435-444, 


204  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

West  of  Danby  Hill  and  Clark  Mountain  is  the  Tinmouth 
valley,  much  of  which  is  low,  swampy  land.  It  joins  at  the  north 
with  the  valley  of  Clarendon  River. 

At  the  southern  end  of  the  Tinmouth  valley,  one  mile  west  of 
Danby  Four  Corners,  black  phyllite  or  schist  outcrops  along  the 
road  to  Tinmouth  for  a  mile  and  a  half  north  of  the  Pawlet  road. 
Between  the  schist  and  Danby  Pond  there  appears  to  be  some 
"marbly"  limestone.  About  two  miles  southwest  of  Danby  Four 
Corners  is  blue  limestone.  The  phyllite  is  precisely  Hke  that 
which  occurs  in  the  ridge  at  the  east  and  in  the  various  localities 
described  on  previous  pages. 

Three  miles  north  of  the  road  from  the  Corners  to  Pawlet, 
and  75  rods  west  of  the  Tinmouth  road,  and  along  the  same  gen- 
eral contours  northward  are  exposures  of  strongly-sheared  lime- 
stone or  marble.  At  many  places  these  ledges  of  marble  do  not 
at  all  appear  like  the  outcropping  edges  of  thick  masses  of  the 
rock,  but  rather  as  a  broken  covering  to  some  rock  on  which  it 
lies.  Two  miles  west  of  the  Tinmouth  road,  within  the  main 
range,  at  the  southern  end  of  Harrington  Hill,  is  what  appears  to 
be  an  isolated  patch  of  marbly  rock  lying  on  the  terrigenous 
formation.  On  the  trip  which  was  made  to  inspect  these  rela- 
tions there  was  not  time  to  map  the  country  with  the  care  neces- 
sary to  show  the  extent  to  which  the  marble  or  its  probable 
equivalent  occurs  in  scattered  exposures  over  the  hills,  or  to  as- 
certain to  just  what  extent  it  is  interrupted  at  the  surface  by  the 
phyllite  along  the  western  edge  of  the  Tinmouth  valley.  It  was 
hoped  that  there  would  be  another  opportunity  to  investigate  the 
relations  within  the  hills  at  the  west.  There  are  indications  of 
considerable  massive  quartzite  on  the  west  side  of  the  Tinmouth 
valley  in  the  general  vicinity  of  Tinmouth. 

On  the  eastern  slope  of  Clark  Mountain  are  patches  of  bluish 
limestone  not  so  severely  metamorphosed  as  the  marbles  of  the 
region  usually  are.  They  appear  to  rest  on  the  schist.  In  the 
valley  of  Otter  Creek  on  the  west  side  of  the  stream  at  South 
Wallingford  are  exposures  of  the  heavy  marble,  including  a 
quarry.  Adjacent  to  these  and  extending  eastward  from  them 
are  the  interbedded  rocks  of  the  Lower  Cambrian,  and  east  of 
these,  less  than  a  mile  away,  is  the  quartzite  of  the  plateau. 

The  interbedded  members  of  the  Lower  Cambrian  continue 
northward  from  South  Wallingford  on  the  east  side  of  Otter 
Creek,  forming  conspicuous  hills  two  miles  north  of  the  village. 
In  these  the  beds  have  been  compressed  so  that  they  now  stand  on 
end.  Northward  between  these  exposures  and  the  village  of 
Wallingford  the  quartzite  of  Green  Hill  comes  down  close  to  the 
railroad  track  with  a  low  but  good  scarp  on  the  wept. 

Westward  across  the  creek  and  its  flat  flood  plain,  near  Wal- 
lingford village,  three-fourths  of  a  mile  away,  is  a  sharp  ascent 
from  the  level  of  the  plain  which  the  writer  at  the  time  of  in- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  205 

spection  put  down  as  a  probable  fault.  It  runs  along  the  eastern 
base  of  the  ridge  that  extends  northward  from  the  Clark  Moun- 
tain portion  for  4  or  5  miles.  The  rock  along  this  slope  is  schist 
or  phyllite;  but  northward,  southwest  of  Clarendon  village,  the 
place  of  the  sharp  slope  is  taken  by  a  more  gentle  one  and  that  of 
the  phyllite  by  quartzite.  The  base  of  the  sharp  slope  referred 
to  is  marked  by  swampy  land  for  part  of  its  extent  and  south- 
west of  Wallingford  by  Fox  Pond. 

Westward  from  Wallingford  village  over  the  ridge  the  sur- 
face rock  is  largely  schist  or  phyllite,  with  some  quartzite.  The 
boundaries  of  these  two  rocks  were  not  traced  along  the  ridge 
for  4  miles  north  of  the  road  that  crosses  the  ridge  from  Wal- 
lingford village  to  Tinmouth  village,  except  on  the  west  slope 
where  the  road  descends  diagonally  across  massive  quartzite. 

Clarendon  village  in  the  Otter  Creek  valley  is  4  miles  north 
of  Wallingford  village.  West  of  the  former  the  eastern  slope 
of  the  ridge  that  lies  to  the  west  rises  rapidly  but  gradually  from 
the  level  of  the  creek  over  quartzite  which  shows  the  structure 
given  in  Bgure  17.  About  300  or  400  yards  up  the  slope  from  the 
main  road,  members  of  the  interbedded  series  of  the  Cambrian  ap- 
parently lie  on  the  quartzite  as  they  do  on  the  eastern  slope  of 
Danby  Hill.  The  prevailing  surface  rock  over  the  ridge  to  Chip- 
penhook  is  quartzite ;  but  on  the  west  slope  east  of  Chippenhook 
appears  the  interbedded  series  which  continues  westward  into 
the  valley  of  Clarendon  River.  At  Chippenhook,  in  the  valley 
and  east  bank  of  Clarendon  River,  the  beds  of  the  interbedded 
series  stand  at  a  higher  angle  than  farther  east.  A  similar  rela- 
tion was  noted  between  the  quartzite  of  Clark  Mountain  and  the 
interbedded  series  lying  west  of  it.  It  appears  that  these  rocks, 
both  in  their  larger  and  smaller  folds,  show  overturning  west- 
ward. 

Southeast  of  Clarendon  Springs,  east  of  the  road  that  ascends 
from  Chippenhook  over  Boardman  Hill,  black  schist  or  phyllite 
ledges  are  intermingled  with  others  of  gneissic-looking  quartzite, 
and  the  two  are  often  together  and  in  contact  in  the  same  ledge. 
Northward  down  the  hill  to  the  bed  of  a  brook  is  massive,  thick- 
bedded,  jointed  quartzite,  dipping  easterly  at  a  low  angle.  East- 
ward along  a  road  that  follows  the  brook  to  Otter  Creek  is  quartz- 
ite dipping  easterly  and  apparently  extending  to  the  eastern  base 
of  the  ridge.     The  rock  is  often  gneissic  at  the  east. 

East  of  Clarendon  Springs  at  Flat  Rock  and  northward,  east 
of  the  road  over  Boardman  Hill  to  Center  Rutland,  is  quartzite, 
often  gneissic  in  appearance,  having  essentially  the  same  rela- 
tions to  schist  or  phyllite  as  noted  above,  but  with  the  resistant 
ledges  of  the  quartzite  often  forming  knolls  of  higher  elevation 
than  the  adjacent  schist  and  giving  a  strong  impression  of  quartz- 
ite pushed  over  on  schist. 


206  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

The  road  from  Chippenhook  to  Center  Rutland  over  Board- 
man  Hill  makes  a  steep  ascent  diagonally  across  the  western  slope 
of  the  ridge.  The  outcropping  rock  along  it  is  phyllite  or  schist, 
specimens  of  which  at  most  places  would  not  be  distinguishable 
from  similar  rock  at  scores  of  places  in  the  Sudbury  hills.  The 
schist  outcrops  appear  in  the  road  about  a  mile  north  of  Chip- 
penhook and  thence  continue  along  the  road  and  east  of  it  and 
farther  north  also  in  ledges  west  of  it,  to  a  point  about  a  mile 
and  one-fourth  north  of  Flat  Rock.  Here  the  quartzite,  which 
was  mentioned  above,  crosses  the  road  to  Boardman  Hill  whence 
it  continues  northward  west  of  the  road  and  along  it  towards 
Center  Rutland.  Some  outcrops  of  the  phyllite  appear  east  of 
the  western  outcrops  of  quartzite.  The  dip  of  the  quartzite  and 
the  apparent  dip  of  the  schist  is  easterly.  The  boundary  between 
schist  and  quartzite  is  in  fact  irregular  and  modified  somewhat 
by  promiscuous  intermingling  or  interchanging  of  areas  of  schist 
and  quartzite.  Near  and  on  Boardman  Hill  the  ledges  of  quartz- 
itic  schist  or  thin-bedded  quartzite  show  severe  crumpling  with 
small  folds  in  more  or  less  recumbent  position,  but  more  massive 
beds  farther  east  have  not  been  deformed  so  much,  although  the 
quartzite  has  taken  on  frequently  a  gneissic  structure. 

West  of  Flat  Rock  and  Boardman  Hill  the  western  slope  of 
the  ridge  descends  to  the  valley  of  Clarendon  River,  first  over 
schist,  then  on  marble.  Outcrops  of  the  latter  were  noted  near 
Austin's  house  between  the  900  and  1,000  feet  contours.  Marble 
outcrops  occur  east  and  west  of  the  stream  and  at  one  place  along 
the  road  to  West  Rutland  the  rock  is  quarried  (Clarendon  Marble 
Co.)  and  at  other  places  east  of  the  stream  it  has  been  opened. 
But  northward  along  the  road  the  phyllite  appears  and  intei*venes 
between  the  marble  exposures  just  mentioned  and  the  great  quar- 
ries of  the  Vermont  Marble  Co.  at  West  Rutland  along  the  valley 
of  the  head  stream  of  Castleton  River.  To  what  extent,  if  any, 
the  marble  is  interrupted  in  its  north  and  south  surface  extension 
between  Clarendon  Springs  and  Center  Rutland  was  not  inves- 
tigated. 

Along  the  ridge  north  of  Boardman  Hill  the  quartzite  was 
traced  to  within  a  mile  of  Center  Rutland,  but  was  not  followed 
down  the  northern  slope  of  the  hill  where  it  presumably  occurs ; 
for  the  rock  was  noted  in  the  bed  of  the  creek  at  Center  Rutland. 

About  a  mile  north  of  Tinmouth  village  a  gap  in  the  range 
leads  to  Middletown  Springs.  Along  the  road  the  terrigenous 
rocks  at  the  northern  end  of  Tinmouth  Mountain  are  precisely 
like  those  in  the  hills  at  the  north  in  Hubbardton,  Sudbury  and 
Orwell,  and  while  lithological  distinctions  may  be  drawn  among 
the  rocks  in  both  places  any  separation  on  the  basis  of  age  seems 
impossible  at  the  south  as  at  the  north,  as  well  as  between  the 
two.  About  a  mile  west  of  the  Tinmouth-Chippenhook  road, 
"marbly"  limestone  appears.     Its  boundaries  were  not  traced.     It 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  207 

seemed  surrounded  with  terrigenous  rocks,  at  the  surface.  No 
limestone  was  found  at  Ira,  although  it  is  reported  from  there 
and  undoubtedly  would  have  been  seen  by  careful  search. 

As  previously  mentioned,  east  of  Otter  Creek  near  South 
Wallingford  the  steep  slope  of  the  Green  Mountain  plateau  bends 
northeastward.  The  edge  is  marked  southeast  of  Wallingford 
by  a  high  scarp  known  locally  as  the  "White  Rocks."  While 
the  valley  thus  widens  out  between  the  plateau  and  the  ridge  that 
extends  northward  from  Danby  Hill,  the  western  boundary  in 
the  eastern  quartzite  swings  to  the  valley  and  is  now  marked  east 
of  Otter  Creek  and  south  of  Wallingford  village  by  the  western 
edge  of  "Green  Hill"  which  has  the  same  general  relation  to  the 
plateau  that  the  valley  quartzite  has  at  Bennington,  except  that 
at  north  there  are  scarps  in  the  valley  as  well  as  in  the  plateau. 
The  scarps  at  the  north  have  been  freshened  by  ice  action. 

The  rocks  were  not  examined  north  of  Wallingford  village 
east  of  Otter  Creek,  between  that  town  and  Rutland.  In  the 
valley  of  Otter  Creek  no  marble  was  seen  between  South  Walling- 
ford and  Rutland ;  nor  was  any  noted  between  South  Walling- 
ford and  Danby.  But  the  interbedded  rocks  were  frequently  seen 
from  Danby  Borough  northward  to  Wallingford  village,  more 
particularly  east  of  Otter  Creek. 

The  quartzite  which  was  noted  in  the  bed  of  the  creek  at 
Center  Rutland  was  found  two-thirds  of  a  mile  north  in  the  cut 
of  the  Rutland  R.  R.  Later  on  a  trip  from  Rutland  city  over 
Pine  Hill  to  Proctor  village  this  rock  was  traced  from  a  point 
about  one  mile  north  of  the  outskirts  of  the  city,  from  outcrops 
just  west  of  the  Pittsford  road,  up  the  eastern  slope  of  Pine  Hill 
along  the  cable  line  to  the  schist  outcrops  on  the  summit  and 
higher  western  slope  at  the  northern  end  of  the  hill.  Schist 
was  noted,  apparently  in  place,  while  ascending  the  eastern  slope 
along  a  wood  road  to  the  cable  line. 

The  quartzite  on  the  eastern  slope  dips  easterly  and  eastward 
is  overlain  apparently  conformably  by  dolomitic  limestone,  in 
which  one  reading  gave  the  strike  due  north  (magnetic)  and  the 
dip  42°  easterly.  As  examined  just  east  of  the  Pittsford  road 
the  limestone  at  places  contains  many  grains  and  sometimes  larger 
patches  of  silica.  The  quartzite  apparently  has  some  interbedded 
schist. 

North  of  Pine  Hill  there  is  apparently  a  structural  break. 
Pine  Hill  occupying  the  upthrow  side. 

At  the  northern  end  of  Pine  Hill  the  sharp  descent  on  the 
west  is  over  schist  for  a  distance  and  then  over  calcareous  rocks 
that  apparently  belong  to  the  dolomite  and  dolomite-quartzite 
members  of  the  Lower  Cambrian,  which  around  Proctor  and 
southward,  east  and  west  of  Otter  Creek,  are  in  association  with 
marble.  The  interbedded  rocks  were  traced  northward  into  Pitts- 
ford, where  their  relations  to  the  marble  is  the  same  as  it  is 


208  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

around  Brandon;  outcrops  of  the  marble  occur  east  of  the  west- 
ern margin  of  the  interbedded  rocks.  South  of  the  Brandon 
township  line,  except  for  a  brief  distance  in  Pittsford,  the  west- 
ern margin  of  the  interbedded  rocks  was  not  minutely  traced 
in  its  relation  to  outcrops  of  marble.  Around  Proctor  the  inter- 
bedded rocks  will  often  be  seen  in  almost  vertical  attitude  as  has 
been  described  for  the  areas  both  north  and  south.  Two  and  a 
half  miles  north  of  Proctor  they  were  seen  lying  in  an  almost 
flat  position.  South  of  Proctor  marble  outcrops  and  has  been 
opened  along  the  lower  western  slopes  of  Pine  Hill  east  of  Otter 
Creek.  Between  these  exposures  and  other  marble  outcrops  far- 
ther west  the  calcareous  membefs  of  the  Lower  Cambrian  inter- 
vene, affording,  apparently,  another  instance  of  exposure  of  mar- 
ble by  the  erosion  of  its  covering  of  Lower  Cambrian  rocks. 

Otter  Creek  has  clearly  availed  itself  of  structural  features 
in  its  course,  particularly  around  Rutland.  At  the  city  it  turns 
from  a  northerly  course  to  a  westerly  one  as  far  as  Center  Rut- 
land, whence  it  again  flows  northerly  west  of  Pine  Hill  through 
Proctor  and  on  to  Pittsford. 

The  marble  and  the  dolomite  and  interbedded  rocks  of  the 
valley  of  Otter  Creek,  north  of  Center  Rutland,  lie  between  the 
mass  of  Pine  Hill  and  a  ridge  of  schist  and  phyllite.  This  ridge 
northward  is  broken  to  a  slight  extent  topographically,  but  ge- 
ologically joins  with  the  quartzite-phyllite  rocks  in  eastern  Pitts- 
ford township,  which  in  turn  join  with  those  of  Brandon  on  the 
north  and  Hubbardton  on  the  west.  On  the  ridge  west  of  Proc- 
tor village  are  some  patches  of  "marbly"  rock  and  a  mile  west  of 
Fowler,  farther  north,  is  another  patch  of  calcareous  rock  sur- 
rounded by  the  schist.  Northward  the  terrigenous  rocks  are 
faulted  at  places  west  of  Brandon,  as  has  been  described  on  pre- 
vious pages,  against  the  sheared  blue  limestones  and  marbles  and 
finally  disappear  under  these  rocks  in  northern  Sudbury  town- 
ship. 

West  of  the  schist  ridge  just  mentioned  lie  the  marbles  of 
West  Rutland  between  this  ridge  and  the  main  mass  of  ter- 
rigenous rocks  lying  to  the  west  in  Castleton.  In  these  marbles 
have  been  found  bluish-gray  rocks  with  abundant  specimens  of 
Maclurea  magna.  The  calcareous  rocks  of  the  West  Rutland 
valley  extend  as  a  narrow  band  about  five  miles  long  and  termi- 
nate at  the  present  surface  at  the  north  and  south  against  the 
phyllite  formation. 

Westward  the  phyllite  rocks  along  the  Castleton  River  valley 
give  place  at  the  surface  to  the  slates  of«  Castleton  and  Fairhaven, 
but  the  slates  are  more  or  less  associated  with  phyllite  rocks  just 
as  they  are  north  of  Castleton  in  Hubbardton  and  Sudbury  and 
north  of  Fairhaven  in  Benson,  as  described  on  previous  pages. 

Summary.  Some  of  the  details  and  some  of  the  general 
relations  which  have  just  been  given  in  the  preceding  description 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  209 

of  certain  portions  of  the  townships  now  being  considered  have 
been  noted  by  other  writers.  The  studies  which  have  been  only 
in  part  briefly  presented  by  the  writer,  were  made  for  the  pur- 
pose of  gaining  from  direct  observation  first-hand  knowledge  by 
which  comparison  could  be  made  with  the  rocks  and  their  rela- 
tions at  other  places  and  really  represent  only  a  part  of  what  it 
was  hoped  to  make.  They  are  offered  for  their  general  bearing 
on  the  question  of  the  interpretation  of  the  broad  structural 
features  of  western  Vermont. 

In  general  it  appears  that  the  structural  features  of  the  dif- 
ferent portions  of  the  Vermont  valley  will  have  to  be  reconciled 
with  each  other.  The  assumption  of  similar  genesis  with  respect 
to  the  main  features  of  the  valley  throughout  would  seem  to  rest 
upon  strong  probability. 

It  further  appears  from  features  which  have  been  and  will 
be  cited  that  the  general  structural  relation  of  plateau  to  valley  is 
the  same  all  along  the  contiguous  margins  of  the  two.  The  Ver- 
mont valley  now  in  its  relation  to  the  plateau  is  a  downthrow  re- 
gion and  a  dismembered  portion  of  the  plateau.  Probably  this 
statement  expresses  only  a  portion  of  the  truth,  however,  as  it 
appears  probable  that  the  western  side  of  the  valley  is  faulted 
also,  so  that  the  valley  is  primarily  a  great  structural  trough 
between  the  plateau  on  the  east  and  the  mountains  on  the  west. 
If  this  is  the  fact  then  in  our  thinking  we  must  in  imagination  by 
taking  account  of  probable  displacement  and  erosion  restore  the 
valley  floor  to  its  approximate  original  position  and  in  such  way 
strive  to  visualize  what  the  former  relation  of  the  plateau  and 
the  masses  west  of  the  valley  would  have  been  through  the  con- 
necting mass  which  was  displaced. 

It  may  be  asked,  what  evidence  is  there  that  the  western 
side  of  the  valley  is  faulted?  West  of  Brandon  there  is  evidence 
to  show  that  the  sheared  limestones  and  marbles  north  and  east 
of  the  phyllite  hills  are  downfaulted,  the  fault  being  sometimes 
in  the  marble  and  sometimes  between  the  phyllite  and  the  marble. 
There  is  evidence  on  the  east  of  Mt.  Anthony  in  Bennington  and 
Pownal  of  downfaulting  of  the  valley  rocks.  It  happens  that 
along  the  west  side  of  the  valley  it  is  not  so  easy  to  tie  up  some 
formation  in  the  valley  floor  with  one  in  the  Taconic  range  as  it 
is  in  the  case  of  the  valley  quartzite  with  respect  to  similar  rock 
in  the  plateau.  At  Dorset  Mountain,  however,  we  see  the  marble 
at  its  high  level  there  and  find  its  counterpart  beneath  the  surface 
of  the  valley.  With  the  fairly  satisfactory  evidence  at  the  east 
of  downfaulting  why  assume  that  Dorset  Mountain  has  primarily 
been  thrust  up  with  respect  to  the  valley  ?  Dorset  Mountain  pre- 
sents evidence  by  itself  of  displacement  between  it  and  adjacent 
rocks  on  the  north  and  south.  This  fact  rather  argues  against 
any  such  idea  as  that  the  whole  region  west  of  the  plateau  margin 
is  downfaulted  with  respect  to  the  plateau,  which  view  might 


210,  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

permit  the  explanation  of  the  valley  as  an  erosion  feature  purely. 
There  is  no  reason  for  selecting  Dorset  Mountain  out  of  the 
Taconic  region  and  assuming  for  it  upthrow  displacement  with 
respect  to  adjacent  rocks.  On  the  whole  it  seems  most  probable 
to  the  writer  that  in  view  of  the  displacement  between  plateau 
and  valley  there  was  also  displacement  between  the  valley  and 
the  masses  now  at  the  west  and  that  such  is  the  significance  of 
the  relations  shown  at  Dorset  Mountain  and  at  other  places. 

The  marble  is  at  different  levels.  In  the  valley  it  appears 
to  be  at  about  the  same  level  at  most  places,  but  varies  somewhat 
even  there.  In  the  Dorset  Mountain  mass  it  is  much  higher  and 
perhaps  repeated.  In  Tinmouth  valley  it  is  intermediate  between 
its  level  in  Dorset  and  in  the  main  valley.  This  general  state- 
ment of  the  levels  at  which  the  marble  occurs  refers  only  to  the 
general  Vermont  valley  region  and  its  extension  into  the  Cham- 
plain  lowland  and  passes  by  for  the  moment  the  detached  patches 
in  the  hills  at  the  west. 

The  surface  of  the  Vermont  valley  is  controlled  at  various 
places  by  the  peculiar  structural  conditions  which  there  prevail. 
North  of  Bennington  and  through  to  Manchester,  and  in  fact 
practically  all  along  its  eastern  border,  the  Lower  Cambrian  rocks 
shape  its  surface.  North  of  Dorset  Mountain  the  main  general 
valley  widens  and  new  features  appear. 

The  steep  northern  slopes  of  Dorset  Mountain,  except  as 
affected  by  general  weathering,  stream  incision,  and  by  drift,  pass 
rather  abruptly  to  a  more  gradual  and  gentle  slope,  which  except 
for  the  incision  of  Mill  Brook  and  the  lateral  erosion  consequent 
upon  it,  continues  without  important  change  of  level  to  the  sum- 
mit of  Danby  Hill  and  northward  to  Pine  Hill  and  the  schist 
ridge  west  of  it  in  Rutland.  This  somewhat  varying  level  marks 
a  surface  of  intermediate  altitude  in  a  ridge  intermediate  between 
the  plateau  and  the  main  mass  of  the  Taconic  range.  This  ridge 
is  bounded  on  the  east  for  most  of  its  length  by  the  Otter  Creek 
valley  and  on  the  west  by  the  valleys  of  Tinmouth  Channel  and 
parts  of  Clarendon  and  Castleton  Rivers. 

North  of  Dorset  Mountain  a  region  marked  out  by  an  east- 
west  line  just  north  of  the  mountain,  a  north-south  hne  running 
probably  along  the  western  edge  of  the  Tinmouth  valley  and  its 
extension,  another  north-south  line  at  the  east,  and  an  irregular 
line  at  the  north,  represents  an  area  of  downthrow  in  which  the 
displacement  has  been  differential.  The  intermediate  ridge  just 
mentioned  is  on  the  downthrow  side  with  respect  to  Dorset 
Mountain,  the  plateau  and  the  main  mass  of  schist  at  the  west, 
and  on  the  upthrow  side  with  respect  to  the  rocks  underlying 
Otter  Creek.  Its  relation  to  the  narrow  valley  on  the  west  of 
it  may  be  discussed  later.  Pine  Hill  is  probably  on  the  upthrow 
side  with  respect  to  the  area  in  Pittsford  north  of  it  and  poten- 
tially so  with  respect  to  the  valley  of  Otter  Creek  south  of  it. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  211 

One  of  the  first  efforts  at  a  restoration,  such  as  has  been 
suggested,  of  the  original  conditions  prevaihng  between  plateau 
and  the  mountains  at  the  west  would  be  to  get  the  surface  of  the 
valley  quartzite  back  at  its  former  level,  so  to  speak.  If  this 
were  done  all  along  the  valley  and  lowland,  beginning  at  Ben- 
nington and  extending  to  Brandon,  a  great  mass  of  rocks  would 
be  lifted.  Along  the  eastern  portion  of  the  valley  at  least  the 
calcareous  members  of  the  Lower  Cambrian  that  now  lie  at 
places  on  the  valley  quartzite  would  be  elevated  to  a  level  some 
distance  above  the  eroded  surface  of  the  plateau  and  would  in 
effect  restore  a  part  of  the  surface  now  gone  from  the  plateau. 
Some  account  would  have  to  be  taken  of  erosion  of  the  plateau, 
but  the  quartzite  is  a  resistant  rock. 

Passing  for  the  present  what  particular  effects  would  be  pro- 
duced in  the  southern  portion  of  the  valley  and  in  the  region  of 
the  Cham'plain  lowland,  and  considering  only  what  would  be  the 
results  in  the  regions  of  Dorset  Mountain  and  the  part  of  the 
valley  north  of  it  to  Pitts  ford,  the  elevation  of  the  upper  surface 
of  the  valley  quartzite  even  to  the  present  sky  line  of  that  forma- 
tion in  the  plateau  would  bring  it  to  about  the  level  of  the  schist- 
quartzite  mass  that  partially  caps  Dorset  Mountain.  The  cal- 
careous members  of  the  Cambrian  would  be  above  the  quartzite. 
What  is  now  beneath  or  adjacent  to  the  quartzite  which  would  be 
elevated  with  it? 

In  such  an  attempt  at  reconstruction  there  must  necessarily 
be  a  large  number  of  elements  of  uncertainty.  This  number 
should  be  reduced  as  much  as  possible. 

We  may  assume,  but  only  assume,  that  there  has  been  no 
displacement  between  the  marble  of  Dorset  and  that  in  the  valley 
other  than  that  which  dropped  the  latter ;  or  in  other  words,  that 
the  plateau  and  Dorset  retain  their  relative  positions  practically 
unchanged  since  the  displacement  of  the  block  between  them. 

If  no\v  we  take  the  relations  shown  at  South  Wallingford  of 
interbedded  rocks  resting  on  marble  at  their  face  value,  and 
recall  the  conditions  east  of  Brandon  and  those  which  apparently 
obtain  around  Proctor  and  Pittsford,  it  appears  that  in  the  neigh- 
borhood of  Dorset  Mountain  we  have  probable  overlap  of  the 
calcareous  members  of  the  Lower  Cambrian  on  the  marble.  At 
Pine  Hill  we  see  a  terrigenous  mass  consisting  of  a  sort  of  con- 
glomerate and  a  quartzite  with  interbedded  schist,  overlain  by 
dolomitic  limestone  and  interbedded  rocks  lying  against  marble  at 
the  west  with  the  interbedded  series  apparently  .lying  on  the 
marble  just  west  of  the  hill.  The  sequence  which  we  have  from 
the  plateau  through  Pine  Hill  and  the  Center  Rutland  marble 
strip  is  not  very  different  from  that  which  is  present  east  of 
Brandon ;  but  at  the  south,  west  of  the  Center  Rutland  marble 
strip,  we  have  conditions  different  from  those  near  Brandon  in 


212  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

the  presence  of  a  ridge  of  schist  intervening  between  the  marble 
of  the  Center  Rutland  strip  and  that  of  the  West  Rutland  strip. 

In  restoring  the  conditions  in  thdvalley  east  of  Dorset  Moun- 
tain it  would  appear  that  between  the  quartzite  as  elevated  and 
the  mass  of  Dorset  there  should  intervene  a  narrow  block  of 
marble  with  interbedded  rocks  overlying  it.  In  Dorset  Mountain, 
schist  with  thick  beds  of  quartzite  tops  the  marble  and  the  rela- 
tive meridianal  positions  of  the  different  rocks  are  made  to  cor- 
respond between  the  restoration  of  plateau  to  Dorset  Mountain 
and  what  now  prevails  near  Pine  Hill. 

The  schist  on  Dorset  Mountain  and  northward  has  usually 
been  regarded  as  younger  than  the  marble.  The  fact  that  it 
lies  on  the  marble  probably  by  itself  is  not  a  sure  indication  that  it 
is  younger ;  for  it  now  appears  practically  certain  that  the  marble 
is  at  many  places  in  the  valley  overlain  by  Lower  Cambrian  cal- 
careous rocks.  The  argument  assumes  that  the  marble  is  younger 
than  the  interbedded  series  of  the  Cambrian,  evidence  for  which 
is  had  in  the  specimens  of  Maclurea  magna  of  the  West  Rutland 
quarries,  if  the  evidence  as  deduced  from  surface  continuity  for 
the  Brandon  region  and  as  afforded  from  other  relations  is  not 
conclusive. 

On  what  does  the  marble  of  Dorset  Mountain  rest?  It  is 
sometimes  represented  as  passing  beneath  a  schist  formation  as 
though  it  continued  indefinitely  westward  from  the  Vermont  val- 
ley in  that  relation  to  the  mass  of  schist  composing  the  Taconic 
range  and  its  foothills,  and  as  though  it  passed  at  depth  discon- 
formably,  or  otherwise,  into  other  calcareous  rocks  with  Cam- 
brian dolomites  at  their  base.  When  the  marble  is  found  among 
the  terrigenous  rocks  of  the  hills  west  of  the  valley  it  is  explained 
as  emerging  from  beneath,  or  as  interbedded  with  the  schist. 

Examination  of  some  of  the  patches  of  "marbly"  Hmestone 
within  the  terrigenous  rocks  west  of  the  valley  often  does  not 
convey  the  idea  of  its  being  beneath,  or  of  its  being  interbedded ; 
but  gives  the  distinct  impression  that  it  rests  on  the  phyllite 
formation.  In  fact  it  would  appear  that  marble  rests  on  schist 
and  that  the  latter  rests  on  marble.  The  point  would  naturally 
be  raised  as  to  whether  the  schist  above  is  the  same  as  or  like 
that  below :  that  is,  are  limestone  and  phyllite  usually  really  inter- 
stratified  ? 

At  West  Mountain  in  Shaftsbury  and  at  many  other  places 
within  areas  which  are  mapped  as  "Berkshire  Schist,"  the  pre- 
vailing terrigenous  rocks  are  not  distinguishable  at  all  from  those 
of  other  areas  on  which  fossiliferous  limestone,  sheared,  blue 
limestone,  or  "marbly"  limestone  now  rest  or  certainly  did  rest 
at  one  time.  In  Brandon,  Sudbury,  Orwell  and  Benson  are  ter- 
rigenous rocks  having  to  limestone  the  relation  just  mentioned, 
which  the  writer  regards  as  so  like  the  phyllites  and  schists  of 
Danby,  Clarendon  and  Rutland,  that  it  is  not  possible  to  make 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  213 

a  sharp  separation.  They  in  fact  join  with  each  other  at  the 
present  surface.  These  terrigenous  rocks  in  Sudbury,  Orwell 
and  other  places  consist  of  interstratified  schists,  phyllites  and 
quartzites.  The  schists  which  top  Dorset  are  interbedded  with 
thick  beds  of  massive  quartzite.  Those  which  form  the  ridge 
from  Danby  Hill  northward  also  seem  to  be. 

If  we  accept  as  valid  the  evidence  that  has  been  offered  on 
previous  pages  for  a  wide  extension  of  calcareous  rocks,  includ- 
ing the  marble  along  the  Vermont  valley  and  the  Champlain 
lowland,  over  a  terrigenous  formation  that  is  over  large  areas 
quite  similar  in  its  general  characters  and  of  probably  similar  age, 
and  if  on  this  basis  we  accept  the  idea  that  a  section  from  the 
plateau  westward  is  essentially  the  same,  whether  it  is  along  a 
parallel  passing  through  Leicester,  Whiting  and  Shoreham,  or 
along  one  through  Dorset  Mountain,  Rupert  and  westward,  ex- 
cept for  differences  of  metamorphism  of  the  limestone  or  the 
terrigenous  rock  and  for  differences  in  the  present  attitudes  of 
the  rocks,  with  consequent  scarcity  of  hmestone  on  schist  at  the 
south  and  consequent  small  exposure  of  schist  through  limestone 
at  the  north,  and  perhaps  also  for  differences  due  to  original 
lateral  variation  in  the  terrigenous  rock,  then  if  we  think  of  the 
phyllite  of  the  Sudbury  hills  passing  beneath  the  marble  of  Bran- 
don we  may  also  think  of  it  as  passing  beneath  the  marble  of 
Dorset  Mountain  and  that  of  the  valley  east  of  the  mountain.  In 
connection  with  conditions  in  the  Vermont  valley,  we  especially 
recall  that  at  places  among  the  hills  at  the  west  masses  of  lime- 
stone which  rest  on  the  terrigenous  formation  have  also  been 
preserved  through  protection  by  downfaulting. 

The  Vermont  Report  (page  412)  states  that  "the  limestone 
from  West  Dorset  is  continuous,  through  a  notch  on  the  west 
end  of  Mount  Eolus,  with  the  limestone  and  marble  in  the  central 
part  of  Danby,  upon  the  west  range  of  the  limestone  formation." 
The  map  so  shows  it.  Along  the  valley  of  the  Mettawee  a  few 
miles  due  west  from  Dorset  Mountain,  as  discussed  on  a  subse- 
quent page,  limestone  (here  the  dove-colored  rock  with  gray 
dolomite)  rests  on  the  phyllite.  The  Vermont  Report  (page  412), 
apparently  on  the  authority  of  the  elder  Hitchcock,  gives  the 
limestone  as  extending  from  Dorset  over  the  mountain  to  Sand- 
gate. 

Accepting  the  idea  of  overlap  along  the  eastern  edge  of  the 
valley,  from  such  evidence  as  we  have,  we  have  nothing  to  tell 
us  how  far  the  marble  extends  eastward  beneath  the  older  rocks. 
The  important  fact  is  that  of  overlap.  If  the  marble  lies  on  a 
quartzite-phyllite  formation  and  practically  the  same  kind  of 
rocks  now  lie  on  the  marble  at  any  place  in  or  west  of  the  Ver- 
mont valley,  one  of  the  ways  in  which  this  relation  might  possibly 
be  explained,  involves  an  extension  of  the  quartzite-phyllite  for- 


214  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

mation  on  which  the  marble  lies  eastward  beneath  the  margin  of 
the  overlap. 

An  effort  has  been  made  to  get  before  the  reader  a  certain 
amount  of  evidence  which  goes  to  show  a  widely-prevailing  rela- 
tion between  apparently  related  calcareous  rocks  and  a  terrige- 
nous formation  that  is  similar  over  wide  areas  and  which  in- 
dicates that  the  normal  position  is  limestone  on  the  phyllite 
formation.  Attention  was  then  called  to  the  resemblance,  as  it 
appears  to  the  writer,  which  such  terrigenous  formation  has  to 
similar  rocks  that  have  an  inverse  relation  to  the  limestone  and 
that  now  at  certain  places  rest  on  it,  that  is,  on  marble. 

It  seems  to  the  writer  that  a  certain  amount  of  assumption  is 
involved  when  the  schist  on  the  limestone  is  called  younger. 
We  have  seen  that  superposition  may  not  be  regarded  as  conclu- 
sive evidence  in  this  region.  The  age  of  the  "Berkshire  Schist" 
seems  to  have  been  determined  indirectly  in  all  cases,  either  from 
field  relations  or  in  some  other  way.  From  relations  which  it  has 
to  limestones  at  many  places  it  would  seem  clearly  on  such  a 
basis  to  be  older  and  in  no  wise  interbedded.  It  has  apparently 
been  assumed  that  the  Cambrian  dolomite  and  dolomite-quartzite 
series  passes  directly  beneath  marble  along  certain  parts  of  the 
Vermont  valley  and  that  the  calcareous  rocks  thus  make  up  a 
conformable  or  disconformable  "Cambro-Ordovician"  limestone 
series  on  which  lies  a  conformable  "Berkshire  Schist."  Such 
views,  in  the  writer's  opinion,  leave  in  the  air  the  explanation  of 
such  relations  as  overlap  of  the  Cambrian  rocks  on  the  marble 
at  numerous  places ;  the  undoubted  superposition  of  related  lime- 
stones including  marbles  on  terrigenous  rocks  which  are  similar 
to  and  many  of  which  are  correlated  with  the  "Berkshire  Schist," 
and  the  relations  which  have  been  described  in  more  or  less  detail 
for  Orwell,  Benson,  Sudbury  and  Whiting.  They  further  seem 
to  ignore  great  thrusts,  or  at  least,  the  wide  extent  of  obvious 
movement  of  older  on  younger  rocks,  which  the  region  every- 
where exemplifies. 

Even  if  the  general  and  normal  superposition  of  the  lime- 
stone on  the  terrigenous  formation  over  a  wide  region  is  admitted, 
it  is  not  of  course  necessary  on  that  account  to  give  up  the  idea 
that  the  schist  resting  on  marble  is  younger  than  the  marble, 
because  it  is  conceivable  that  conditions  of  deposition  permitted 
the  succession  from  limestone  to  terrigenous  rock,  or  from  ter- 
rigenous rock  to  limestone  and  again  to  terrigenous  rock,  perhaps 
over  a  wide  region.  Nothing  in  this  summary  has  been  said 
about  the  age  of  the  quartzite-phyllite  formation  except  that  it 
often  appears  to  be  older  as  a  whole,  as  now  eroded,  than  the 
limestone  which  rests  on  it,  including  the  marble.  Further  than 
the  suggestions  offered  on  previous  pages  the  consideration  of 
its  probable  age  may  be  postponed. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  215 

One  of  the  things  that  is  perhaps  confusing  in  explaining 
the  relations  along  the  Vermont  valley  on  the  basis  of  overlap 
by  thrust  of  older  rocks  on  younger  ones  is  the  fact  that  erosion 
apparently  nowhere  has  uncovered  a  clear  overlap  of  Cambrian 
quartzite  on  marble ;  something  sharp  and  distinct  like  that  of  the 
quartzite  on  the  "Utica"  at  Burlington.  Another  thing  that  is 
bound  to  be  confusing,  if  it  occurs,  is  overlap  of  terrigenous  rocks 
on  other  entirely  similar  rocks,  by  thrust. 

It  has  been  implied  above  that  the  marble  which  underlies 
the  valley,  for  example,  that  at  South  Wallingford,  has  been 
dropped  from  a  higher  level.  North  of  Rutland  the  marble  on 
the  meridian  of  that  of  South  Wallingford  is  apparently  covered 
by  the  quartzite-schist  and  its  overlying  calcareous  rocks  in  Pine 
Hill.  At  South  Wallingford  only  the  interbedded  series  can  be 
seen  to  have  any  relation  like  that  of  overlap  on  marble. 

The  marble  along  Otter  Creek  north  of  Dorset  Mountain  has 
been  assumed  by  some  to  pass  beneath  the  intermediate  ridge 
lying  to  the  west  and  to  emerge  in  the  Tinmouth-Clarendon  River 
valley.  This  is  the  view  given  in  the  Vermont  Report.  By  others 
the  intermediate  ridge  has  been  regarded  as  an  anticline  under- 
lain by  the  basal  Cambrian  quartzite  and  the  underlying  pre- 
Cambrian  and  overlain  by  the  "Stockbridge"  limestone  and 
"Berkshire  Schist."  Overthrust  of  Cambrian  quartzite  on  schist 
is  described  and  indicated  and  inclusion  of  limestone  and  schist 
in  the  older  rocks  is  shown  as  occurring  by  the  younger  rock 
being  faulted  down  into  the  older  rock. 

The  structural  pattern  of  the  valley  north  of  Dorset  Moun- 
tain is  unquestionably  complicated  and  hard  to  analyze.  It  seems, 
however,  that  one  of  the  first  steps  would  be  to  try  and  make  a 
restoration  on  the  basis  of  the  valley  being  a  downfaulted  region. 
Along  the  eastern  side  the  Cambrian  quartzite  and  interbedded 
schist  could  be  thought  of  as  elevated,  carrying  the  Cambrian  cal- 
careous rocks  above  it  and  presumably  at  places  at  least,  as  at 
Pine  Hill,  the  subjacent  marble  to  a  higher  level.  In  other  areas 
with  more  or  less  indeterminate  boundaries  on  account  of  irregu- 
larity of  early  overlap  the  interbedded  rocks  of  the  Cambrian  and 
its  subjacent  marble  could  be  imagined  as  elevated.  In  still  other 
areas,  probably  in  different  measure  according  to  amount  of  dis- 
placement, the  schist-quartzite  masses  of  the  intermediate  ridge 
would  be  elevated,  and  by  assumption,  subjacent  marble  with  it. 

By  these  imaginary  processes  it  would  seem  that  we  should 
get  an  extensive  mass  of  marble  over  the  area  north  of  Dorset 
Mountain,  approximately  back  to  former  levels  one  of  which  is 
now  marked  by  the  marble  of  the  Dorset  mass.  It  would  seem, 
too,  that  the  quartzite-schist  of  the  intermediate  ridge  would  be 
restored  to  a  higher  level  and  on  this  quartzite-schist  with  prob- 
ably some  overlying  "marbly"  limestone  we  should  find  a  capping 
of  dolomite  and  interbedded  rocks,  which  we  have  come  to  asso- 


216  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

date  with  the  Lower  Cambrian,  the  whole  mass  of  Cambrian 
showing  the  buckling  so  characteristic  of  the  interbedded  series, 
as  has  been  described  so  many  times.  We  should  recall  that  the 
same  kind  of  deformation  exhibited  by  the  quartzite  on  the  inter- 
mediate ridge  is  shown  also  by  the  quartzite  east  of  Otter  Creek, 
and  that  in  fact  one  is  the  replica  of  the  other.  At  places  we  now 
find  lying  on  the  schist  of  the  intermediate  ridge,  small  patches 
of  limestone  younger  than  the  Cambrian,  sometimes  fossiliferous, 
sometimes  "marbly,"  and  it  would  appear  that  some  of  these  were 
formerly  overlain  by  quartzite,  which  in  turn  was  and  is  now  at 
places,  overlain  by  the  interbedded  rocks  of  the  Cambrian.  In 
some  places  we  now  find  all  these  various  rocks  within  the  space 
of  a  few  acres,  intermingling  at  the  present  surface,  but  in  rela- 
tions which  suggest  that  the  schist  is  lowest,  the  "marbly"  or  other 
limestone  next,  the  quartzite  next  and  finally  the  interbedded 
series.  Underneath  all,  presumably,  is  other  massive  marble. 
Farther  west  in  the  Tinmouth  valley  are  some  indications  that 
the  interbedded  series  rests  on  massive  marble,  but  this  is  not  so 
certain ;  the  massive  marble  may  be  deeper  down.  Except  for 
erosion  or  lack  of  it,  and  minor  details,  this  brief  description 
would  seem  to  apply  to  the  whole  ridge  from  Danby  Hill  north 
to  Center  Rutland.  At  Center  Rutland  the  massive  quartzite 
apparently  swings  to  Pine  Hill  and  does  not  touch  the  West 
Rutland  ridge;  but  the  latter  presumably  gives  marble  at  depth, 
then  the  schist  and  on  top  of  the  latter,  patches  of  marbly  lime- 
stone, with  possibly  som^e  of  the  interbedded  rocks  along  its  east- 
ern base. 

It  would  seem  from  such  a  restoration  as  has  been  attempted 
that  north  of  Dorset  Mountain  there  would  have  been  overlap  of 
Cambrian  rocks  as  far  west  as  Tinmouth  valley,  with  younger 
rocks  underneath.  Sometimes  this  overlap  apparently  carried  the 
interbedded  rocks  on  the  marble  with  no  quartzite  or  schist  in- 
tervening. Sometimes  interbedded  quartzite  may  have  been  car- 
ried over  on  schist  with  limestone  or  "marbly"  rock  intervening. 
Sometimes  quartzite  with  overlying  calcareous  rocks  may  have 
been  carried  over  the  schist  with  "marbly"  limestone  intervening. 

On  the  general  idea  of  overlap  of  Cambrian  rocks  as  just 
developed,  recalHng  the  conditions  north  of  Dorset  Mountain,  it 
would  seem  that  a  restoration  at  Dorset  Mountain  would  involve 
^an  overlap  on  its  summit  of  calcareous  members  of  the  Cam- 
brian series,  perhaps  on  younger  limestones  that  have  been  eroded. 

The  ideas  developed  up  to  this  point  clearly  depart  from  the 
view  that  the  Cambrian  rocks  of  the  valley,  as  now  exposed,  are 
members  of  a  series  that  is  subjacent  to  the  schist-phyllite  forma- 
tion, and  suppose  rather  that  a  portion  of  the  Cambrian  floor 
has  moved  from  the  east  over  on  younger  rocks  and  now  lies  by 
unconformable  thrust  overlap  on  younger  strata.  Overlap  seems 
fairly  plain ;  its  extent  is  less  certain.     From  what  has  been  said 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  217 

above  it  is  further  regarded  as  probable  that  the  normal  position 
for  the  marble  is  above  a  terrigenous  formation  like  that  which 
caps  it.  On  this  view  the  terrigenous  formation  is  also  beneath 
the  marble  of  Dorset  Mountain  and  extends  eastward  beneath 
the  margin  of  the  overlap  of  older  rock  and  also  beneath  the 
valley  marble,  for  an  indeterminate  distance,  but  perhaps  not  very 
far.     How  far  is  wholly  problematical. 

Now  it  seems  possible  to  imagine  that  the  conditions  which 
seemingly  would  be  present,  after  such  a  restoration  as  has  been 
attempted  was  made,  over  the  region  under  discussion,  could  be 
explained  by  a  series  of  thrust  displacements.  The  quartzite- 
phyllite  formation  and  its  overlying  probably  younger  limestone 
were  broken  by  reverse  faults  which  probably  were  usually  minor 
thrusts,  and  along  the  planes  of  these  thrusts  the  quartzite-phyllite 
formation  and  the  overlying  younger  limestone  were  driven  west- 
ward through  and  over  similar  rocks  until  they  came  to  overlie 
the  younger  limestone  at  the  west.  Or  the  plane  may  conceivably 
have  cut  in  such  way  as  to  carry  the  phyllite  against  other  but 
similar  terrigenous  rocks — cutting  downward,  for  example,  at 
places  beneath  the  limestone,  or  into  the  terrigenous  rock,  and 
pushing  the  sliced-ofif  portion  on  the  "toe"  of  the  thrust.  It  seems 
not  difficult  to  imagine  that  there  may  have  been  several  such 
thrusts,  some  of  which  may  now  be  covered  eastward  and  some 
of  which  may  have  been  wholly  or  partly  eroded  westward.  On 
meridians  farther  east  a  series  composed  of  quartzite-phyllite 
with  overlying  dolomite  and  interbedded  rocks  was  broken  by 
reverse  faults  and  finally,  after  ease  of  stress  had  been  partly  ac- 
complished in  this  way,  along  an  extensive,  irregular  plane, 
which  truncated  earlier  planes  within  the  series  at  depth  and  cut 
through  different  members  of  it,  a  great  mass  of  rock  was  driven 
westward  over  previous  thrust  masses  at  the  west  and  may  pos^ 
sibly  at  places  have  overlapped  several  earlier  thrusts.  During 
these'  deformations  probably  some  folding  occurred  as  a  result 
of  compression  and  some  perhaps  as  the  result  of  friction  along 
the  surface  of  movement.  On  the  hypothesis  of  repeated  thrust- 
ing, as  thus  outlined,  the  possibilities  of  some  of  the  marbles 
being  separated  from  each  other  by  thrust  planes  should  be  con- 
sidered. During  this  overriding  may  have  been  the  time  when 
the  marbles  acquired  their  particular  metamorphic  characters 
which  distinguish  them  from  the  apparently  related  rocks  which 
carry  fossils,  or  are  less  metamorphosed,  and  which  lie,  so  to 
speak,  west  of  the  probable  margin  of  the  thrust  overlaps  from 
the  east. 

In  the  section  from  the  plateau  westward  through  Pine  Hill 
apparently  we  should  have,  after  restoration  by  elevation,  quartz- 
ite-schist  with  overlying  dolomite  elevated  along  a  reverse  fault 
against  the  interbedded  dolomites  and  quartzites,  and  the  whole 
series  cut  by  and  resting  along  a  thrust  plane  which  had  cut 


218  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

through  what  is  now  marble  overlying  phyllite  which  together  by 
a  minor  thrust  had  been  previously  and  independently  pushed 
over  other  calcareous  rock  now  represented  by  the  marble  of  the 
West  Rutland  valley,  which  may  have  its  normal  position  on  the 
terrigenous  formation.  These  various  rocks  are  probably  now 
much  disturbed  from  their  thrust  relations  on  account  of  later 
normal  fault  displacements. 

Whenever  the  schist  which  had  thus  been  thrust  was  brought 
by  thrust  or  by  later  normal  faulting  against  phyllite  or  schist 
which  had  been  overridden  it  would  probably  not  be  possible, 
oftentimes,  to  tell  the  two  terrigenous  rocks  apart,  except  possibly 
by  difference  in  metamorphism  of  the  moved  rock. 

,  South  of  Pine  Hill  minor  thrusts  would  have  broken  and 
dislocated  parts  of  the  Lower  Cambrian  series  with  respect  to 
each  other  and  another  deeper  thrust  would  have  truncated  these ; 
but  the  various  thrusts,  cutting  and  thrusting  here  in  different 
ways  from  those  at .  the  north,  would  presumably  have  pro- 
duced the  peculiar  minor  features  present  at  the  south.  The 
overlap  of  Cambrian  on  the  marble  would,  however,  have  been 
produced. 

If  at  some  subsequent  time  these  overthrust  rocks  were 
broken  by  differential  tension  faulting  and  dropped,  as  has  been 
argued,  the  marbles  under  the  overthrust  would  have  been  carried 
down,  except  at  Dorset  Mountain,  perhaps,  and  at  other  places 
south  of  it,  and  after  erosion  we  should  see  the  conditions  as 
they  are  today.  It  seems  possible  that  portions  of  the  main  part 
of  the  Taconic  range  may  be  overthrust  masses  that  are  now 
protecting  younger  limestone  (marble)  at  depth.  West  of  the 
preserved  overthrusts  the  limestone,  because  unprotected,  has 
largely  disappeared  by  erosion. 

BENNINGTON  AND  RUTLAND  COUNTIES. 

Townships  of  Shaftsbury,  Arlington,  Snnderland,  MancLiester,  Dorset, 
Kupert  and  Pawlet. 

(Equinox,   Londonderry,   Wallingford   and   Pawlet  topographic 

sheets.) 

Topography.  The  areas  examined  in  these  townships  lie 
mostly  in  the  Vermont  valley  or  that  of  the  Mettawee  River.  For 
the  most  part  the  topography  has  been  sufficiently  described  in 
speaking  of  the  physiographic  divisions  of  western  Vermont. 

Observations  in  certain  parts  of  the  Vermont  valley  through 
northeastern  Shaftsbury,  Arlington,  Sunderland,  Manchester  and 
Dorset.  The  observations  of  the  writer  to  be  noted  of  the  ex- 
posures and  relations  of  the  rocks  in  the  towns  mentioned  in  the 
heading  of  this  section  were  made  chiefly  along  the  eastern  part 
of  the  Vermont  valley.  The  rocks  along  the  western  part  were 
only  casually  inspected.     It  was  the  purpose  to  make  a  more 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  219 

critical  examination  of  them  later  during  the  same  season  (1918), 
which  illness  prevented,  in  connection  with  the  mountain  rocks 
on  the  west  side  of  the  valley. 

The  surface  covering  is  heavy  along  the  eastern  side  of  the 
valley  most  of  the  way  from  Shaftsbury  to  Manchester.  On  this 
account  it  did  not  prove  possible  to  work  out  much  concerning 
the  precise  interrelationships  of  the  hard  rocks. 

The  interbedded  dolomite-quartzite  series  of  the  Lower  Cam- 
brian as  seen  in  the  eastern  parts  of  Bennington  and  Shaftsbury 
was  traced  northward  into  Manchester  and  it  was  noted  that 
the  rocks  continue  to  show  northward  at  many  places  the  charac- 
teristic topographic  form  of  elongated  arches  which  will  be  de- 
scribed for  the  areas  at  the  south. 

East  of  Shaftsbury  village  the  folds  of  members  of  this 
series  exhibit  overturning  to  the  west  as  was  noted  so  often  far- 
ther south  and  which  is  a  very  characteristic  attitude  which  has 
been  acquired  by  these  interbedded  rocks  along  the  valley.  Plate 
XXXIV  shows  this  overturning  on  a  small  scale  and  in  this  case 
is  a  perfect  repHca  of  what  occurs  all  along  the  valley  on  a  larger 
scale,  but  which  in  the  larger  folds  is  obscured  by  abrasion. 
Any  further  description  of  these  hills  of  the  interbedded  rocks 
throughout  their  extent  from  Shaftsbury  to  Manchester  would 
be  largely  repetition. 

It  should  be  noted  that  the  hills  of  these  rocks  do  not  lie 
snugly  along  the  base  of  the  slope  of  the  Green  Mountain  plateau 
that  fronts  the  valley  on  the  east,  but  are  separated  from  it  by  a 
space  of  varying  width  in  which  there  is  much  modified  and  other 
drift  material. 

East  of  East  Arlington  village,  north  of  "Kansas,"  streams 
have  worn  through  from  75  to  100  feet  of  sand  and  gravel  with- 
out exposing  the  basement  rock.  Plate  XXXIV  shows  the  present 
character  of  some  of  the  kame  and  terrace  covering  that  sur- 
rounds the  hills  of  Lower  Cambrian  rocks  and  apparently  over- 
lies other  parts  of  the  series.  Other  areas  are  bowlder  strewn 
and  have  apparently  a  relatively  thin  covering  of  bowlder  drift. 
The  quartzite  and  overlying  members  of  the  Lower  Cambrian, 
in  relations  like  those  in  Shaftsbury  and  Bennington,  doubtless 
underlie  the  drift  and  the  series  probably  extends  all  along  the 
eastern  side  of  the  valley  through  these  towns. 

Quartzite  was  traced  at  several  places  up  the  steep  slopes  of 
the  plateau.  All  the  relations  indicate  that  the  valley  rocks  are 
dismembered  portions  of  the  plateau  as  is  the  case  at  the  south 
near  Bennington  and  at  the  north  near  Brandon.  Although  the 
quartzite  was  not  noted  in  the  valley  between  Bennington  and 
Manchester  in  actual  surface  outcrops,  southeast  of  Manchester 
the  abundance  of  quartzite  bowlders  over  certain  areas  suggests 
that  the  quartzite  is  not  far  below  the  surface  there. 

"  The  Vermont  valley  widens  out  in  Manchester  and  about  4 
miles  north  of  Manchester  Center,  marble  outcrops  extensively 


220  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

at  the  surface  and  is  worked  in  quarries  at  South  Dorset.  Other 
quarries  have  been  opened  between  South  Dorset  village  and  the 
southern  base  of  the  Dorset  Mountain  mass  and  still  others  high 
up  on  the  southern  slopes.  While  the  quarries  at  South  Dorset 
are  in  some  cases  below  the  1,000  feet  contour,  some  of  those 
near  Owl's  Head  on  Dorset  Mountain  are  about  on  the  1,900 
feet  contour. 

The  different  elevations  at  which  the  marble  is  worked  on 
the  south  of  the  Dorset  Mountain  mass  and  the  topographic  out- 
lines suggest  a  probable  displacement  by  which  the  marble  of  the 
valley  has  been  dropped  from  a  higher  level. 

At  the  old  Norcross  quarry  (see  plate  XXXV)  a  certain 
thickness  of  dolomite  now  rests  with  sharp  contact  on  the  marble 
and  is  well  exposed  in  the  north  face  of  the  old  part  of  the  quarry. 
The  dolomite  is  infolded  somewhat  with  the  surface  of  the  mar- 
ble. The  rock  has  much  the  same  relation  that  a  similar  rock 
has  to  a  marble  in  Swinington's  quarry  at  Leicester  Junction, 
which  is  right  on  the  western  margin  of  the  calcareous  members 
of  the  Lower  Cambrian  series  in  the  township  of  Leicester. 

In  the  quarries  examined  around  South  Dorset  the  marble 
shows  the  same  internal  deformation  in  the  form  of  flow  struc- 
tures that  marks  the  marble  nearly  all  the  way  along  the  Vermont 
valley.  It  is  in  contrast  to  the  interbedded  series  of  the  Lower 
Cambrian  just  as  it  is  near  Brandon.  It  is  more  metamorphosed 
in  most  cases  than  the  dolomite  that  at  certain  places  lies  on  it. 

Observations  along  the  valley  of  the  Mettazvee  in  Dorset, 
East  Rupert,  North  Rupert  and  Pawlet  to  Granville,  N.  Y.  Scat- 
tered observations  were  made  along  the  valley  of  the  Mettawee 
from  South  Dorset  to  Granville,  N.  Y.  Some  features  of  interest 
were  observed. 

Limestone  or  marble  was  noted  along  the  road  a  mile  east 
of  East  Rupert. 

From  East  Rupert  to  North  Rupert  the  hill  slopes  along  the 
valley  road  were  only  casually  inspected,  but  no  difference  was 
noted  between  the  terrigenous  rocks  that  compose  them  and  those 
which  have  been  described  on  previous  pages  for  the  hills  in  the 
northern  part  of  the  range. 

Northwest  of  North  Rupert  the  hill  slopes  on  the  south  side 
of  the  road  were  more  carefully  examined.  Here  are  the  black  and 
light-colored  phyllites,  the  crinkled  and  more  massive  quartzites, 
making  up  precisely  the  same  assemblage  as  to  be  found  in  the 
Sudbury  and  Orwell  hills.  They  cannot  be  told  apart.  Two  and 
a  half  miles  northwest  of  North  Rupert,  south  of  the  valley  road 
to  Pawlet,  at  the  end  of  a  short,  blind  road,  limestone  rests  on 
the  phyllite.  A  mile  north,  south  of  the  main  road,  are  excellent 
exposures  of  dove-colored  limestone  with  gray  patches  of  dolo- 
mite and  other  exposures  in  which- the  gray  rock  makes  up  prac- 
tically the  entire  visible  mass.     More  careful  examination  than 


S5 

3P 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  221 

the  writer  was  able  to  give  on  a  day's  tramp  would  undoubtedly 
disclose  more  extensive  outcrops  of  the  calcareous  rock  in  a  rela- 
tion to  the  phyllite  similar  to  that  which  has  been  noted  at  so 
many  places. 

From  the  outcrops  last  described,  the  hill  slopes  along  the 
road  through  Pawlet  give  the  phyllites.  At  Indian  Hill  and  a 
mile  east  of  it  along  the  road  are  crinkled  quartzites  and  light- 
colored,  siliceous  phyllites. 

From  North  Pawlet  a  fine  series  of  scarps  can  be  seen  bound- 
ing Burt,  Cleveland  and  Lincoln  hills  and  Pond  Mountain  on  the 
west,  and  an  east-west  scarp  on  the  south  of  Haystack  Mountain. 

Summary.  Whatever  its  meaning  may  be,  a  section  from  the 
Green  Mountain  plateau  east  of  Manchester  carried  northwest- 
erly through  Dorset  along  the  valley  of  the  Mettawee  to  Granville 
gives  a  repetition  of  the  section  from  the  Green  Mountain  plateau 
east  of  Brandon  carried  over  the  Sudbury  and  Orwell  hills  with 
certain  differences  that  are  less  impressive  than  the  resemblances. 
The  Lower  Cambrian  rocks  have  practically  the  same  relation  to 
the  marble,  the  calcareous  rock  rests  on  essentially  the  same  ter- 
rigenous formation,  and  the  latter  presents  the  same  difHculty  of 
division  into  parts  on  the  basis  of  age  or  other  characters.  More 
slate  appears  in  the  southern  section  (west  of  North  Pawlet) 
and  because  of  size  of  exposure  permits  easier  arbitrary  field 
division  and  mapping,  but  similar  slate  occurs  in  the  northern 
section  at  several  places. 

The  Verm,ont  valley  and  eastern  slopes  of  Dorset  Mountain 
in  Dorset  and  southern  Danby.  The  valley  narrows  north  of 
Manchester  between  the  plateau  and  the  mass  of  Dorset  Moun- 
tain. The  interbedded  series  continues  northward  in  the  narrow 
space  between  the  steep  western  slope  of  the  plateau  and  the 
abrupt  eastern  slope  of  Dorset. 

In  East  Dorset  village  along  the  road  and  just  above  the 
buildings  of  the  East  Dorset  Marble  Co.  are  beds  of  dolomite. 
At  the  later  place  they  pitch  in  a  northerly  direction.  The  writer 
was  unable  to  decide  what  this  dolomite  represents,  unless  it  is 
below  the  interbedded  series  and  a  part  of  the  Cambrian. 

North  of  the  road  from  East  Dorset  village  up  the  eastern 
slope  of  the  mountain  (Green  Peak)  and  some  distance  up  the 
slope  the  interbedded  series  is  plainly  visible.  The  writer's  notes 
give  a  westerly  dip  for  these  beds  at  a  point  well  up  the  slope. 
Schistose  limestone  with  some  slaty  rock  were  noted  a  short 
distance  up  the  eastern  slope  from  East  Dorset  station  near  the 
road. 

The  eastern  slope  of  the  mountain  impresses  one  as  being 
bounded  by  normal  faults.  The  great  apparent  thickness  of  cal- 
careous rocks  that  appears  along  the  slope  may  be  due  to  dis- 
placements along  more  than  one  plane  as  the  rocks  now  in  the 
valley  at  the  east  and  south  were  dropped,  leaving  the  marble 


222  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

and  associated  rocks  after  erosion  in  view  at  the  higher  levels 
and  the  interbedded  rocks  at  the  surface  on  the  lower  slopes  and 
in  the  valley  where  the  marble  is  now  concealed  beneath  them. 
The  idea  of  faulting  is  borne  out  by  the  general  relations  round- 
about as  well  as  by  the  aspect  of  the  mountain  slope  itself. 

The  marble  on  the  east  face  of  Green  Peak  and  northward 
is  quarried  at  about  the  same  level  as  that  at  Owl's  Head.  The 
fact  of  the  same  general  level  for  the  quarries  may  be  made  out 
from  the  valley  road.  At  the  Dorset  Hill  quarry  the  same  feat- 
ures of  metamorphism  that  have  been  mentioned  for  the  marble 
elsewhere  were  noted,  as  also  the  facts  that  while  bedding  is  now 
largely  gone  and  flow  structure  and  crystallinity  have  been  in- 
duced, the  marble  stratum  or  mass  lies  in  a  fiattish  position  as  a 
whole,  indicating  that  the  metamorphic  structures  which  it  shows 
were  probably  induced  under  confinement  of  the  mass  and  sug- 
gesting that  similarity  of  relations  or  conditions  prevailed  over 
the  wide  area  in  which  similar  marble  now  occurs  while  these 
features  were  in  process  of  formation. 

Overlying  the  marble  in  Green  Peak  and  northward  practi- 
cally continuously  to  Dorset  Peak,  is  the  so-called  "Berkshire 
Schist"  which,  it  is  here  interesting  to  note,  is  really  a  mass  of 
interbedded  schistose  and  phyllitic  rocks  with  thick  beds  of  quartz- 
ite  and  which  as  a  whole,  except  for  their  aspect  of  somewhat 
greater  metamorphism,  do  not  look  conspicuously  unlike  the 
quartzite-phyllite  assemblage  of  the  Hubbardton,  Benson,  Orwell 
and  Sudbury  hills. 


Figure  18.  Sections  to  show  different  attitudes  at  different,  places  of  the 
interbedded  series  of  the  Lower  Cambrian  along  the  summit  of  an  anti- 
clinal ridge  in  the  valley  between  Dorset  Mt.  and  the  plateau. 

In  the  valley  two  miles  north  of  East  Dorset  and  east  of  Dor- 
set Pond,  on  the  strike  of  the  northward-pitching  dolomites  at 
at  East  Dorset  station,  light-gray  dolomite  of  the  interbedded 
series  forms  a  ridge.  The  rock  is  rather  thinly-bedded  at  many 
places.  Along  the  summit  or  upper  portions  of  the  western 
slope  the  beds  may  at  one  place  be  seen  dipping  rather  gently 
easterly,  at  another  westerly,  and  still  another  standing  on  end  or 
dipping  easterly  at  a  high  angle  (figure  18).  There  has  clearly 
been  overturning  to  the  westward,  as  is  indicated  by  the  variations 
in  the  dip  of  these  anticlinal  beds  along  and  near  the  axis  of  the 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  223 

fold.  The  same  structure  in  these  interbedded  rocks  is  shown  in 
the  narrow  valley  here  as  in  the  wider  portions  at  the  south  and 
north. 

North  of  North  Dorset  a  clear  scarp  defines  the  basal  portion 
of  the  eastern  slope  of  Dorset  Peak.  The  ridge  of  interbedded 
rocks  described  in  the  preceding  paragraph  continues  northward 
east  of  the  railroad  track  for  two  miles  north  of  North  Dorset 
and  then  drops  gradually  off  into  the  lowland  of  Otter  Creek. 
Near  its  northern  termination  it  is  marked  on  the  west  by  a 
moderate  but  steep  scarp.  West  of  the  track  and  the  highway, 
a  hill  of  the  same  rocks  rests  against  the  scarp  at  the  base  of 
Dorset  with  a  low  scarp  on  the  south.  These  rocks  appear 
greatly  crushed. 

In  the  Vermont  valley  in  Dorset  one  finds  in  the  same  rocks 
evidence  of  strong  compression  and  also  of  displacement  by 
normal  faulting.  Along  the  lower  contours  some  of  the  scarps 
have  been  cleaned  apparently  at  a  relatively  recent  date.  Ero- 
sion prior  to  the  glacier  had  so  softened  the  outlines  of  the  higher 
eastern  slopes  of  Dorset  that  although  they  are  now  steep,  the 
probable  fault  planes  do  not  now  emerge  as  pronounced  scarps 
even  after  ice  action. 

The  observer  is  impressed  in  Dorset,  as  elsewhere,  with  the 
contrast  between  the  plainly-bedded  although  withal  strongly- 
folded  Lower  Cambrian  rocks  and  the  severely  altered  marble, 
and,  in  addition,  senses  some  important  structural  significance  in 
the  presence  of  the  high  mass  of  this  Taconic  mountain  flanked 
by  Lower  Cambrian  quartzite  so  close  to  the  plateau,  and  the 
narrow  valley  in  between  surfaced  with  the  upper  members  of 
the  Lower  Cambrian  series  which  also  extend  up  the  eastern  slope 
of  Dorset  Mountain. 

BENNINGTON  COUNTY. 

Towns  of  Pownal,  Stamford,  Bennington,  Woodford,  Shaftsbury  and 

Glastenbury, 

(Bennington  and  Hoosic  topographic  sheets.) 

The  geological  relations  in  southwestern  Bennington  County 
were  examined  by  the  writer  in  1912  and  made  the  subject  of  a 
paper  entitled,  "Notes  on  the  geology  in  the  vicinity  of  Benning- 
ton, Vt."^  The  map  and  descriptions  therein  given  included  the 
township  of  Bennington,  the  major  parts  of  Pownal  and  Shafts- 
bury,  and  portions  of  Stamford,  Woodford  and  Glastenbury.  It 
will  therefore  be  convenient  to  review  under  one  heading  certain 
relations  described  in  the  paper  mentioned  which  bear  upon  the 
present  discussion,  as  well  as  to  place  on  record  some  later  ob- 
servations made  in  the  region  and  to  offer  some  modifications  of 
conclusions  previously  offered. 

*  Ninth  Report  of  the  State  Geologist,  1914. 


224  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Topographic  features.  This  area  includes  the  southern  por- 
tion of  the  Vermont  valley,  which  is  hemmed  in  on  the  east  by 
the  steep  slope  of  the  plateau  except  where  this  is  cut  by  the 
valley  of  Walloomsac  Brook,  East  of  Bennington  and  north  of 
Walloomsac  Brook  the  western  margin  of  the  plateau  is  offset 
to  the  west  about  two  miles  from  its  course  south  of  the  stream. 

The  valley  narrows  south  of  Bennington  and  is  intercepted 
by  a  ridge  of  schist  which  separates  it  from  the  valley  of  Hoosic 
River  that  enters  Vermont  from  the  Berkshire  valley  in  Massa- 
chusetts. This  schist  ridge  abuts  against  the  plateau  in  Pownal. 
Thence  it  extends  northwestward  and  terminates  in  Mt.  Anthony 
in  Bennington.  The  valley  which  comes  down  froiji  the  north 
through  the  towns  of  Manchester,  Sunderland  and  Shaftsbury  is 
bounded  on  the  west  by  a  high  range  which  terminates  west  of 
Shaftsbury  Center  in  West  Mountain.  Between  West  Mountain 
and  Mt.  Anthony  is  a  wide  open  valley  area  which  marks  the 
extension  of  the  Vermont  valley  into  the  Hudson  valley  region. 

Relations  southeast,  south  and  southwest  of  the  town  of 
Bennington.  In  Stamford  Mountain  a  gneiss  that  is  believed  to 
be  of  pre-Cambrian  age  is  exposed  at  many  places.  Flanking 
this  gneiss  on  the  west  and  also  extending  around  the  southern 
end  of  the  mountain  into  Massachusetts  and  then  northward  into 
Vermont  again  on  the  eastern  side  of  the  mountain  is  quartzite, 
which  at  many  places  in  what  appear  to  be  basal  beds  is  a  massive, 
coarse,  white,  granular  rock  or  a  massive,  compact,  thick-bedded, 
brown  formation.  This  passes  upward  into  thin-bedded,  schistose 
quartzite. 

Glastenbury  Mountain,  north  of  Stamford  Mountain,  is  also 
flanked  on  the  west  by  scarps  of  quartzite.  Faults  separate  these 
mountain  masses  from  each  other  and  bound  them  on  the  west. 
At  the  bases  of  the  scarps  on  the  west  of  the  plateau  lies  a  series 
of  rocks  which,  when  all  members  are  present,  has  a  quartzite  at 
the  base,  essentially  similar  to  that  of  the  plateau,  overlain  by  a 
certain  thickness  of  dolomitic  limestone,  which  is  succeeded  by  an 
interbedded  series  whose  members  are  sometimes  dolomites, 
sometimes  calcareous  quartzites,  and  sometimes  almost  pure 
quartzites.  Unless  disturbed  these  rocks  apparently  are  con- 
formable. 

When  the  series  just  mentioned  was  first  described  by  the 
writer,  owing  to  the  limited  time  which  was  spent  in  areal  map- 
ping and  lack  of  opportunity  to  check  up  certain  portions  of  the 
area,  it  was  not  possible  to  speak  positively  respecting  the  west- 
ward extension  of  the  series  and  its  present  western  surface 
boundary.  Much  of  the  calcareous  rock  outcropping  in  limited 
exposures  through  the  heavy  surface  mantle,  in  the  western  half 
of  the  valley,  both  north  and  south  of  Bennington,  was  simply 
termed  limestone,  in  the  absence  of  certainty  as  to  correlation 
with  the  interbedded  series  or  its  subjacent  dolomitic  limestone, 
or  of  any  fossil  evidence  as  to  age. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  225 

As  surface  outcrops  this  interbedded  series  is  present  in 
greatest  force  and  is  best  exhibited  northeast  of  Bennington.  As 
first  mapped  by  the  writer  it  was  shown  as  a  rather  regular  strip 
about  two  miles  wide  along  the  eastern  side  of  the  valley  north- 
east of  Bennington  and  as  a  somewhat  narrower  strip  southeast 
of  Bennington,  with  its  western  boundary  and  the  relation  of 
the  calcareous  members  to  the  quartzite  not  clearly  defined. 
South  of  Bennington  a  strip  about  two  miles  wide  was  shown  as 
"limestone  formation,"  with  only  two  rather  limited  exposures 
of  the  inbedded  rocks  at  somewhat  widely  separated  places  along 
the  eastern  edge  of  the  strip.  At  one  of  these  places,  which  is 
southeast  of  Barber's  Pond,  the  rocks  are  overlain  by  a  black, 
shiny,  graphitic-looking  phyllite,  which  appeared  conformable  to 
the  underlying  beds.  This  is  the  only  place  in  western  Vermont 
which  the  writer  has  noted  where  the  interbedded  series  is  over- 
lain by  a  schist  or  phyllite. 

In  Pownal  the  calcareous  rocks  of  the  valley  are  intercepted 
or  interrupted  at  the  present  surface  by  the  schist  of  Mason  Hill 
and  by  the  quartzite  of  the  plateau  which  come  together  along  a 
fault  plane. 

From  their  relation  to  the  quartzite  in  which  Lower  Cam- 
brian fossils  have  been  found  the  calcareous  rocks  of  the  series 
just  described  are  regarded  as  of  Lower  Cambrian  age. 

Some  revision  of  the  writer's  previously-held  ideas  has 
proved  necessary  for  the  extension  of  the  Lower  Cambrian  rocks 
around  Bennington.  Observations  which  were  made  during  a 
short  trip  in  the  season  of  1920,  after  a  further  acquaintance  with 
Vermont  rocks  had  been  gained,  may  be  oflfered  here  as  some  of 
them  have  an  important  bearing  on  the  present  paper. 

Just  south  of  Main  street  in  Bennington,  near  the  cemetery, 
dipping  easterly  at  an  angle  of  about  54°,  are  beds  which  were 
originally  called  simply  limestone,  but  which  now  are  regarded 
as  members  of  the  interbedded  series.  Similar  beds  outcrop 
along  the  road  leaving  Main  street  for  Camp  corner  and  again 
in  a  quarry  besides  the  road  three-fourths  of  a  mile  south  of 
Main  street.  In  the  latter  place  the  beds  can  be  seen  to  be 
greatly  disturbed  and  standing  at  a  high  angle,  apparently  over- 
turned. One-half  mile  south  of  this  quarry,  on  the  northern 
slope  of  the  hill,  the  same  rocks  lie  in  a  flattish  position,  showing 
hardly  any  buckling  and  apparently  pitching  slightly  to  the  south. 
One  mile  south-southeast  of  these  flattish  beds  the  interbedded 
rocks  stand  on  end  about  40  or  50  rods  west  of  the  old  lumber 
mill  on  South  Stream. 

Within  less  than  a  mile  therefore,  east  and  west  across  the 
strike,  allowing  for  a  few  offsets  north  and  south  within  a  mile, 
the  interbedded  rocks  pass  from  a  closely-compressed  fold 
through  almost  flat  position  to  highly  inclined  beds.  It  is  certain 
that  the  drift  conceals  disturbed  structural  relations  among  these 


226  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

beds.  Along  the  hill  road  from  Bennington  to  Morgan's  corner 
and  in  the  fields  outcrops  are  few.  Along  the  east-west  road 
from  Morgan's  corner  to  the  main  road  from  Bennington  to 
Pownal  were  observed  some  westward-dipping  beds  which  were 
also  apparently  members  of  the  interbedded  series. 

About  two  and  a  half  miles  south  of  Bennington,  just  south 
of  Robinson's  cross-roads  and  west  of  the  main  Pownal  road, 
a  hill  shows  a  series  which  was  examined  and  finally  assigned  to 
the  interbedded  stratum.  The  rocks  are  largely  dolomitic  but 
carry  some  siliceous  beds.  They  dip  westerly  on  the  east  side, 
but  westward  within  the  distance  of  half  a  mile  the  rocks  show 
confusion  and  brecciation  and  then  a  marked  change  in  the  char- 
acter of  the  rock,  which  will  be  described  beyond.  The  confu- 
sion and  brecciation  are  approximately  on  the  line  of  strike  of 
greatly  brecciated  rocks  two  miles  to  the  north  near  Bennington. 

It  further  seemed  to  the  writer  that  certain  calcareous  beds 
and  associated  rocks,  two  and  a  half  miles  south  of  these  out- 
crops in  the  hill  just  described,  north  of  Pownal  Center,  at  the 
base  of  the  hill  road  running  westward  to  Petty  Corner,  also 
belonged  to  this  interbedded  stratum.  Perhaps  a  hundred  and 
fifty  yards  up  the  steep  hill,  in  the  bed  of  the  brook,  south  of 
the  road,  are  quartzite,  schistose  quartzite  and  sericite  schist  or 
phyllite,  apparently  all  conformable  with  each  other  and  dipping 
easterly  at  a  low  angle  near  the  top  of  the  hill.  At  the  top  of  the 
hill  along  the  road  to  Petty  Corner  and  northward  along  the  road 
west  of  Carpenter  Hill  are  ledges  of  sheared  quartzite  and  quartz- 
itic  schist  which  the  writer  now  considers  to  be  of  probable  Lower 
Cambrian  age  from  their  resemblance  to  other  rocks  in  the  re- 
gion. When  first  described  and  mapped  in  1912,  these  rocks 
were  simply  designated  as  a  part  of  the  terrigenous  formation 
that  forms  the  Mt.  Anthony-Mason  Hill  ridge. 

The  writer  would  now  draw  the  western  boundary  of  the 
Lower  Cambrian  calcareous  rocks  of  the  valley,  from  Pownal 
Center  north  to  the  Pownal  township  line,  close  to  the  base  of  the 
schist  ridge. 

The  observer  passing  along  the  main  road  from  Pownal 
Center  towards  Bennington  would  hardly  fail  to  note  the  low 
but  steep,  eastern,  scarp-like  margin  in  the  ridge  which  extends 
from  just  north  of  Pownal  Center  north  to  Carpenter  Hill.  At 
Pownal  Center  the  schist-quartzite  formation  crosses  the  highway 
to  join  the  schist  of  Mann  Hill.  The  scarp  just  mentioned  is 
low  at  Pownal  Center  but  increases  in  height  northward.  At 
some  places  the  members  of  the  calcareous  series  give  a  false 
impression  of  passing  beneath  the  quartzite-schist  formation  of 
the  ridge,  but  at  other  places  they  seem  rather  clearly  to  be  faulted 
against  it.  The  rocks  at  the  surface  of  both  valley  and  ridge 
from  Pownal  Center  to  Carpenter  Hill  now  appear  to  be  mem- 
bers of  the  Lower  Cambrian  series  of  the  general  region.     It  is 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  227 

the  writer's  opinion  that  an  east-west  section  at  the  surface  in  the 
northern  part  of  Pownal  township  from  the  quartzite  of  the 
plateau  across  the  valley  to  and  including  the  terrigenous  rock 
of  the  eastern  part  of  the  ridge  probably  gives  only  Lower  Cam- 
brian rocks. 

In  Pownal  Center  along  the  road  to  North  Pownal  is  a 
schistose  quartzite,  which  from  the  coarseness  of  its  laminations 
might  be  called  a  quartzitic  gneiss.  To  the  writer  it  appeared 
quite  the  same  as  other  rock  found  in  the  plateau  and  at  other 
places  in  the  Taconic  hills.  This  rock  gives  place  westward  to 
blackish,  pyritiferous,  gritty  schist  or  phylHte.  The  latter,  greatly 
crumpled  and  jammed  and  carrying  much  quartz  in  seams  and 
bunches,  occurs  along  the  western  slopes  of  Mann  Hill  and  is 
particularly  well  shown  along  the  highway  and  trolley  road  from 
Pownal  to  North  Pownal  and  in  cuts  along  the  road  from  Pownal 
to  Pownal  Center.  The  rock  at  the  summit  of  Mann  Hill  is  a 
silvery,  often  greenish,  sericite  schist.  Its  apparent  counterpart 
was  observed,  one  and  a  half  miles  north  of  Pownal  Center  in 
the  beds  of  the  brook  coming  down  from  the  hill  south  of  the 
road  from  Petty  Corner  to  the  valley  road,  and  was  there  ap- 
parently interbedded  with  schistose  quartzite,  (see  above). 

The  schistose  quartzites,  gritty  schists  and  black,  pyritiferous 
phyllites  of  this  ridge,  at  least  from  the  latitude  of  Carpenter 
Hill  southward,  bear  close  lithological  resemblance  to  rocks  which 
are  very  common  in  the  hills  of  the  northern  portion  of  the 
Taconic  range  and  which  are  described  above.  The  lighter- 
colored,  finer-grained,  more  homogenous,  siliceous  phyllites  com- 
mon at  the  north  were  not  so  frequently  observed  in  the  exposures 
examined  in  Pownal. 

It  is  very  hard  to  decide  on  the  basis  of  lithology  alone 
whether  all  the  schist  and  phyllite  belong  to  one  formation.  It 
seems  clear  that  field  relations  among  the  various  rocks  may 
simulate  something  very  different  from  what  they  really  are  on 
account  of  complex  deformation  and  that  in  the  absence  of  definite 
criteria,  assignment  must  be  made  on  the  basis  of  probability.  It 
has  been  particularly  noted  above  that  in  the  Taconic  hills  farther 
north  in  Benson,  Orwell,  Sudbury  and  Brandon  the  black  phyl- 
lites, finer-grained,  light-colored,  sihceous  phyllites,  grits  and 
schists  appear  to  pass  into  one  another  at  the  surface  and  that  it 
becomes  practically  impossible  to  discover  any  particular  arrange- 
ment or  field  relations  among  any  of  them  that  could  be  used  to 
separate  them  as  belonging  to  different  formations  or  terranes. 
Moreover,  in  the  Bennington  region  on  West  Mountain  in  Shafts- 
bury,  the  schist  formation  carries  the  lighter-colored  phyllite  with 
the  other  members  and  it  appears  to  be  still  an  open  question 
whether  the  schist  formation  of  this  mountain  is  in  whole  or  in 
part  Lower  Cambrian  as  mapped  by  Walcott,  or  Ordovician  as 


228  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

mapped  by  Dale  and  formerly  suggested  also  by  the  writer  (1914). 

East  of  Pownal  Center,  on  the  northeastern  slope  of  Alann 
Hill,  limestone  rests  on  the  schist  in  patches  and  the  two  show 
much  intermingling  of  outcops  and  great  confusion.  It  was  not 
possible  to  make  any  correlation  of  the  limestone  on  the  basis  of 
lithology.  The  dip  of  schist  and  limestone  often  seem  the  same. 
Near  Irish  corner  some  early  notes  indicate  the  presence  of  a 
bluish  or  dove-colored  limestone  carrying  gray  patches  Hke  the 
rock  to  be  described  beyond. 

At  North  Pownal  village  a  scarp  of  limestone  begins  a  short 
distance  south  of  the  mill  of  the  Pownal  Lime  Co.  and  runs 
northerly  parallel  with  and  east  of  the  main  road  through  the 
village  to  Whipple's  corner.  In  the  quarries  of  the  Pownal  Lime 
Co.  the  limestone  is  without  definite  bedding,  appears  mashed  and 
shows  black,  pyritiferous  phyllite  overlying  it  and  jammed  in 
with  it.     Plate  XXXVI. 

Under  the  highway,  between  it  and  the  raiload  track,  in 
North  Pownal  village  is  greatly  crumpled  schist  and  the  lime- 
stone seemingly  rests  on  it.  Although  no  contact  was  observed 
here  two  miles  south,  west  of  the  Hoosic  River,  limestone  and 
schist  were  found  in  relations  which  permitted  no  other  inter- 
pretation than  that  the  limestone  rested  on  the  schist  formation. 
East  of  the  high  limestone  hill  in  North  Pownal  village  there 
are  occasional  areas  in  which  limestone  and  schist  outcrops  in- 
termingle at  the  present  surface.  Except  for  some  outcrops  of 
dove-colored  rock  carrying  wavy  stringers  or  layers  of  quartz 
one-half  mile  north  of  Wright  Bridge  corner,  nothing  was  ob- 
served in  the  limestone  in  the  vicinity  of  North  Pownal  that  as- 
sisted in  its  correlation.  In  the  writer's  first  description,  from 
the  general  field  relations  and  apparently  isolated  character  of  this 
limestone,  it  was  regarded  as  a?  faulted  inlier.  It  will  be  referred 
to  again  in  the  discussion  of  the  possible  general  structural  re- 
lations of  the  Bennington  region. 

The  rocks  southeast  of  Bennington  present  some  further 
features  of  structure  and  arrangement  which  should  be  men- 
tioned." 

The  writer's  first  map  showed  the  valley  quartzite  southeast 
of  Bennington  as  bounded  by  a  fault  on  the  west  and  there  is 
still  reason  to  think  from  the  flattish  position  of  the  interbedded 
calcareous  and  quartzitic  rocks  in  the  bed  of  South  Stream,  as 
shown  near  the  lumber  mill  and  nearby,  that  there  is  a  rupture 
between  these  flat  beds  and  the  closely-compressed  similar  rocks 
that  lie  just  west,  as  above  described.  What  was  shown  on  the 
map  as  valley  quartzite  southeast  of  Bennington  may  and  prob- 
ably does  have  at  various  places  some  of  the  calcareous  members 
of  the  series  resting  on  it,  as  is  the  case  in  the  bed  of  South 
Stream ;  but  east  and  southeast  of  Bennington  stream  deposits, 


i^-r; 


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343  ^ 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  229 

carried  into  the  valley  at  the  time  of  glacial  flooding,  largely  con- 
ceal outcrops  except  as  exposed  in  the  beds  of  streams. 

West  of  Harmon  Hill  the  valley  quartzite  from  a  scarp  in 
the  gneiss  dips  gently  westward  and  passes  beneath  this  mantle 
of  stream  deposits,  but  southward  on  the  east,  along  a  strike 
fault  plane  within  the  valley  quartzite,  a  scarp  appears  which 
continuing  southward  rises  in  altitude  and  seems  to  form  the 
main  displacement  that  separates  the  quartzite  of  the  plateau  from 
that  of  the  valley. 

No  apparent  distinction  is  to  be  drawn  between  the  quartzite 
of  the  plateau  and  the  valley.  They  are  the  same  in  all  essential 
characters  and  one  in  fact  merges  into  the  other  where  a  strike 
fault  scarp,  for  example,  along  the  edge  of  the  plateau  dies  away 
into  a  slope  or  monocline  of  the  plateau  quartzite.  In  the  writer's 
first  descriptions  of  this  region  the  obvious  displacements  along 
the  western  edge  of  the  plateau  were  regarded  as  reverse  faults 
by  which  the  gneiss  and  its  overlying  quartzite  were  thrust  up 
into  younger  rocks,  with  repeated  breaks  along  the  strike.  The 
valley  quartzite  was  also  thought  of  as  having  been  elevated  in- 
dependently against  younger  rocks  at  the  west  and  dropped  later 
by  normal  faulting. 

While  there  seem  to  be  probable  ruptures  in  the  rocks  of  the 
valley  by  which  they  now  stand  in  displaced  relations  to  each 
other,  some  modification  of  the  original  description,  which  the 
map  therewith  attempted  to  show,  is  necessary  if  the  Lower 
Cambrian  series  has  the  westward  extension  suggested  in  pre- 
ceding paragraphs. 

In  the  first  description  of  the  region  a  sort  of  assumption 
was  made  that  in  the  vicinity  of  Bennington  there  is  now  a  con- 
siderable but  unknown  thickness  of  Ordovician  terrigenous  rocks 
at  the  surface.  For  the  pre-Cambrian  gneiss  and  its  associated 
Lower  Cambrian  quartzite  to  have  their  apparent  present  relations 
to  the  so-called  younger  masses,  reverse  faulting  was  assumed  to 
have  occurred  along  what  is  now  the  western  edge  of  the  plateau 
and  also  along  planes  that  now  lie  within  the  valley.  To  the 
writer  there  still  appears  much  field  evidence  to  bear  out  the 
idea  of  an  elevation  of  the  pre-Cambrian  floor;  but  the  deforma- 
tion by  which  the  rocks  of  the  Bennington  area,  and  of  western 
Vermont  generally,  came  to.be  as  they  are,  seems  to  be  capable 
of  comprehension,  if  at  all,  only  through  the  study  of  a  wide 
region. 

Southwest  of  Bennington  town  are  numerous  puzzling  rela- 
tions which  bear  upon  both  the  stratigraphy  and  structure  of  the 
region. 

In  an  area  just  southwest  of  Bennington,  bounded  by  South 
street,  Dunham  avenue  and  the  Pownal  road,  occurs  a  bluish 
or  dove-colored  limestone  carrying  many  small  streaks  and 
patches  of  gray  or  chamois  color,  and  associated  with  beds  of 


230  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

gray  or  light  chamois-colored  rock.  These  rocks  have  been  noted 
elsewhere  near  Bennington,  as  will  be  discussed  beyond.  In  one 
outcrop  what  appeared  to  be  a  few  encrinal  stem  fragments  were 
found.  This  rock  is  greatly  sheared  and  near  the  Pownal  road 
carries  bands  of  brecciated  Hmestone.  On  account  of  the  sheared 
structure  it  was  usually  not  possible  to  decide  whether  the  east- 
ward dip  is  that  of  shearing  or  bedding,  in  the  sheared  rock  itself ; 
although  in  one  place  the  dove  and  gray  seemed  clearly  to  be 
interbedded  and  to  dip  easterly.  In  another  place,  perhaps  two 
hundred  yards  south  of  mixed  sheared  and  brecciated  rocks,  and 
along  their  general  strike,  were  somewhat  thick-bedded,  gray 
limestones  dipping  westward  about  20  degrees. 

On  the  east  side  of  the  Pownal  road,  just  south  of  the  junc- 
tion with  Dunham  avenue,  dark,  bluish  limestone  forms  a  ledge 
beside  the  road  and  the  bedding  planes  can  be  distinguished  stand- 
ing at  a  high  angle,  sinuously  bent  along  the  strike  and  apparently 
slightly  overturned.  Strong  shearing  along  many  planes  close 
together  has  greatly  obscured  the  bedding  and  produced  a  sort 
of  slaty  limestone,  (figure  19). 


vv 


Figure  19.  Schematic  section  of  limestone  as  shown  in  a  ledge  near  the 
junction  of  the  Bennington  Center-Pownal  road  and  Dunham  avenue  in 
Bennington.  Limestone  is  close  to  or  involved  in  a  zone  of  crushing 
and  an  easterly-dipping  shearing  has  nearly  obliterated  bedding. 

The  general  strike  of  the  rocks  just  described  is  approx- 
imately north  and  south.  Just  east  of  the  Bennington  Center- 
Pownal  road,  in  the  fields  between  Dunham  avenue  and  the  next 
road  north,  are  many  ledges  over  an  area  several  acres  in  extent, 
in  which  the  limestone  is  greatly  brecciated,  some  of  the  frag- 
ments being  several  inches  in  diameter.  West  of  the  Pownal 
road,  a  few  hundred  yards  northwest  of  these  brecciated  outcrops, 
the  limestone  shows  a  strike  of  N.  81°  W.  and  a  dip  of  24°  south- 
erly which  correspond  in  general  with  the  strike  and  dip  of  the 
heavy  limestones  and  marbles  that  form  the  northern  slope  of 
Mt.  Anthony. 


PLATE  XXXVII. 


Various  fossils  found  in  the  vicinity  of  Bennington.  Numbers  1,  2,  3  and  4 
collected  in  South  Shaftsbury  about  2  miles  north  of  North  Bennington 
village.  Numbers  5  and  6  found  3 1/^  miles  south  of  Bennington  town 
near  Carpenter  Hill.  The  forms  are  described  in  the  text  and  are  re- 
garded as  probably  of  Chazy  age. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  2'6l 

The  sheared  blue  or  dove-colored  limestone  described  above 
is  traceable,  with  long  interruptions,  from  the  outcrops  north  of 
Dunham  avenue  for  two  miles  south-southwesterly  to  some  ledges 
just  west  of  the  road  over  Carpenter  Hill  and  one  mile  south- 
west of  Robinson's  cross-roads.  At  this  place  the  sheared,  patchy, 
dove-colored  rock  and  its  gray  associate  occupy  a  prominent 
knoll  and  form  conspicuous  ledges.  In  the  blue  rock  were  found 
distinct  fossil  markings,  including  a  much-worn  spiral  of  the  size 
of  and  identified  as  Maclurea  magna,  a  smaller  probable  Maclurea 
about  two  inches  in  diameter  (fig.  5,  plate  XXXVII),  and  two 
specimens  like  that  shown  in  number  6,  plate  XXXVII.  On  the 
basis  of  fossils  and  the  resemblance  of  the  rock  to  Chazy  beds 
examined  elsewhere  in  Vermont  these  rocks  are  put  in  that  terrane 
and  regarded  as  probably  Middle  Chazy.  These  rocks  may  be 
represented  east  of  Pownal  Center  near  Irish  Corner,  (see  above). 

North  of  these  outcrops,  along  the  eastern  slope  of  Mt. 
Anthony  the  relations  are  very  obscure.  At  some  places,  partic- 
ularly towards  the  northern  end,  thick-bedded  marbles  dip  west- 
erly into  the  mountain.  The  dip  changes  northward  to  south- 
westerly and  then  to  southerly.  The  mountain  gives  the  appear- 
ance of  being  of  synclinal  structure  with  southerly  pitch  and  of 
being  composed  of  thick  limestone  or  marble  beds  at  the  base, 
which  are  capped  with  schist.  In  a  quarry  in  the  woods  on  the 
east  side  of  the  mountain  and  west  of  the  Everett  mansion,  and 
also  in  Colgate's  quarry  on  the  northwest  side,  along  the  North 
Pownal  road,  a  blue,  crystalline  limestone  stratum  is  seen  to  lie 
just  beneath  the  schist.  This  rock  is  of  uncertain  thickness,  but 
its  strike  and  dip  seem  to  indicate  that  it  is  conformable  to  the 
marbles  below  it.  It  has  not  been  identified  in  the  region  in  any 
other  relations  than  those  just  described. 

Notes  taken  in  1912  indicate  absence  of  noticeable  crushing 
in  the  schist  at  Everett's  quarry  and  describe  the  contact  between 
it  and  the  limestone  as  apparently  conformable.  The  phyllite 
contact  was  described  as  disturbed  at  places  in  Colgate's  quarry, 
although  in  the  northeastern  part  of  the  quarry  a  contact  similar 
to  that  in  Everett's  quarry  could  be  seen.  Internal  deformation 
in  the  schist  is  more  apparent  than  in  the  limestone,  as  perhaps 
would  naturally  be  expected,  whether  in  place  or  not.  The  cal- 
careous rocks  beneath  are  all  highly  crystalline,  but  apparently 
not  deformed  like  the  marbles  that  have  been  noted  as  occurring 
farther  north.  The  contrast  which  the  calcareous  rocks  under- 
lying Mt.  Anthony,  as  well  as  others  which  occur  north  of  it 
and  have  much  the  same  dip,  have  to  the  sheared  and  brecciated 
rocks  of  the  general  vicinity  is  very  marked  and  goes  with  other 
field  relations  to  show  that  most  of  the  strata  of  the  region  have 
been  greatly  disturbed. 

It  should  be  noted  that  the  drift  covering  is  heavy  over  the 
western  part  of  the  valley  south  of  Bennington  and  that  on  that 


232 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


account  much  uncertainty  must  exist  as  to  the  extent  to  which 
Lower  Cambrian  rocks  form  the  hard  rock  substratum  over  this 
area.  Moreover,  there  are  outcrops  of  Hmestone  over  this  re- 
gion which  cannot  be  assigned  with  certainty  to  the  Lower  Cam- 
brian or  to  any  other  terrane.  In  the  Bennington  region  what  is 
immediately  subjacent  to  the  Lower  Cambrian  of  the  valley  can- 
not be  stated  in  any  measure,  so  far  as  the  writer's  knowledge 
goes.  Farther  north  in  Vermont  there  is  good  reason  to  think 
that  the  marble  formation,  whatever  its  age,  is  overlain  by  Lower 
Cambrian  rocks,  as  has  been  shown. 

Ea^t,  northeast  and  north  of  Bennington.  It  has  not  ap- 
peared necessary  to  modify  in  any  essential  particulars  the  rela- 
tions as  described  in  the  author's  previous  paper  for  the  areas 
east,  northeast  and  north  of  Bennington.  They  may  be  very 
briefly  reviewed. 

A  broad  band  of  Lower  Cambrian  rocks  extends  along  the 
eastern  side  of  the  valley  under  the  scarp  of  the  plateau.  In  its 
southern  part,  except  for  a  small  area  of  dolomitic  limestone  and 
overlying  interbedded  rocks  near  Bennington,  quartzite  forms  the 
only  surface  rock  over  a  distance  of  about  4  miles.  In  the  south- 
ern portion  of  the  band  there  is  apparent  a  low  southerly  pitch 
and  the  arrangement  of  quartzite,  limestone  and  interbedded 
rocks  shows  a  conformable  series,  (figure  20). 


Figure  20.  A  generalized  north-south  section  of  the  southern  portion  of  the 
Lower  Cambrian  series  north  of  Bennington,  as  displayed  just  east  of 
the  Bennington  Poor  Farm.  Southward  pitch  exaggerated.  A,  quartz- 
ite ;  B,  dolomitic  limestone  ;  C,  interbedded  dolomites,  calcareous  quartz- 
Ites,    and   quartzites.     All   apparently   conformable. 

The  quartzite  at  its  northern  end  forms  an  anticlinal  buckle 
which  presents  great  ledges  of  white,  granular  quartzite  on  its 
eastern  slopes.  These  have  complete  similarity  with  similar 
quartzite  in  the  plateau  just  east  of  the  valley  quartzite  and  the 
latter  is  looked  upon  as  a  dismembered  portion  of  that  now  flank- 
ing the  plateau.  Southward  towards  Bennington  the  coarser 
quartzite  passes  upward  into  somewhat  thinner  and  more  schistose 
beds  and  thus  gives  the  same  transition  that  may  be  observed  on 
the  western  quartzite  slope  of  "The  Dome"  in  Pownal.  On  the 
west  the  surface  slope  of  this  valley  quartzite  descends  across  the 
edges  of  the  beds. 

At  the  north  the  valley  quartzite  just  described,  in  the  town 
of  Shaftsbury,  is  apparently  cut  off  by  a  tranverse  fault.  The 
quartzite  is  succeeded  abruptly  at  the  surface  by  limestone  which 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  233 

form  a  series  of  arches  elongated  along  the  strike.  Farther  north 
these  are  replaced  by  similar  arches  of  the  interbedded  rocks. 
The  succession  going  north  is  thus  seen  to  be  from  quartzite 
through  limestone  to  the  interbedded  members  of  the  series ;  but 
the  members  have  been  more  disturbed  with  reference  to  each 
other  than  is  the  case  over  the  southern  portion  of  the  strip. 
Moreover,  there  is  apparent  a  series  of  displacements  along  the 
strike  as  well  as  folding  and  faulting  across  it. 

The  arches  described  consist  of  compressed  folds  of  lime- 
stone or  of  the  interbedded  rocks  and  the  beds  frequently  show 
overturning  to  the  west.  The  arches,  including  the  one  in  the 
quartzite  and  those  south  of  Bennington,  are  all  of  similar  genetic 
type.  Northward  these  arches  give  a  characteristic  topographic 
form  to  the  surface  of  much  of  the  Vermont  valley  as  has  been 
mentioned. 

The  members  of  the  Lower  Cambrian  series  north  of  Ben- 
.nington,  just  described,  were  not  positively  identified  in  any  part 
west  of  the  westernmost  exposures  of  its  basal  quartzite  member 
as  this  outcrops  along  the  South  Shaftsbury  road.  Much  surface 
material  covers  the  rock  northwest  of  Bennington  in  the  central 
and  western  parts  of  the  valley.  The  probable  correlation  of  cer- 
tain outcrops  southeast  of  South  Shaftsbury  village  and  in  the 
cuts  of  the  Rutland  R.  R.  north  of  the  village  is  not  now  ap- 
parent. In  the  writer's  map  of  the  Bennington  region  a  probable 
fault  was  shown  as  bounding  the  whole  Lower  Cambrian  series 
on  the  west  from  Bennington  north  to  the  limit  of  the  map.  For 
the  most  part  the  line  to  mark  this  fault  was  drawn  some  distance 
to  the  east  of  South  Shaftsbury  road.  Near  Bennington,  how- 
ever, it  crosses  that  road  at  the  junction  with  the  "Stony  Hill 
road."  The  boundary  as  thus  shown  was  drawn  partly  to  em- 
phasize the  close  age  relations  of  the  rocks  forming  this  broad 
hand  along  the  east  side  of  the  valley  and  partly  to  record  the 
surface  features  indicative  of  displacement  along  their  apparent 
western  margin  at  the  northern  end  of  the  strip. 

It  might  be  noted  here  that  some  fragmentary  outcrops  of 
siliceous  and  dolomitic  rocks  somewhat  resembling  the  members 
of  the  interbedded  series  were  observed  one  and  a  half  miles 
north  of  North  Bennington  village;  but  it  did  not  seem  possible 
to  determine  whether  they  are  in  place. 

West  and  northivest  of  Bennington.  The  general  southerly 
dip  that  marks  the  limestone  and  marble  beds  on  the  northern 
slope  of  Mt.  Anthony  was  traced  northward  to  and  across  the 
Bennington-Hoosic  road  and  was  noted  distinctly  three-fourths 
of  a  mile  northwest  of  the  monument  at  Bennington  Center. 
While  the  rock  in  North  Bennington,  which  will  be  mentioned 
presently,  shows  some  difference  in  strike  and  dip  from  that 
south  of  it,  the  two  bear  resemblances  with  respect  to  absence  of 


234  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

pronounced  internal  deformation  such  as  other  rocks  of  the 
region  show. 

Along  the  banks  and  in  the  bed  of  Paran  Creek,  south  of 
North  Bennington  village,  the  limestone  beds  have  a  strike,  ac- 
cording to  one  reading  selected  as  fairly  representative,  of  about 
N.  80°  E.  and  a  dip  of  about  11°  south-southeasterly.  On  the 
west  side  of  the  road  west  of  the  creek,  opposite  the  office  of  the 
Cushman  Furniture  Company,  are  beds  of  dark  gray  limestone 
ranging  in  thickness  from  about  two  feet  at  the  base  of  the  expo- 
sure to  about  10  inches  or  a  foot  near  the  top.  Similar  beds  out- 
crop just  below  the  dam  of  the  Stark  Paper  Mill  and  above  It 
farther  up  stream.  No  fossils  were  found  and  no  correlation 
seemed  justified  on  any  basis. 

In  Shaftsbury  a  mile  and  a  half  north  of  North  Bennington 
village,  in  the  woods  on  an  east  hill  slope,  southwest  of  Twitchell's 
corner,  were  found  a  few  ledges  of  the  same  sheared,  patchy, 
dove-colored  rock  and  its  gray  associate  seen  southwest  of  Ben- 
nington, west  of  the  road  over  Carpenter  Hill.  The  dip  is  west- 
erly into  the  hill  about  25°  and  the  strike  N.  40°  to  50°  E.  The 
exposures  are  limited  with  drift  all  about.  The  dove-colored  rock 
is  plainly  fossiliferous,  but  the  markings  are  obscure.  Spiral 
lines  and  patches  representing  coiled  shells  of  some  kind  were 
noted  at  several  places.  These  were  hard  to  remove.  Figure  3, 
plate  XXXVII,  gives  an  indication  of  the  markings,  but  some  of 
those  found  at  the  locality  now  being  described  were  much  more 
plainly  shown  to  be  sections  of  coiled  shells.  At  this  locality 
occurs  a  thin  bed  with  abundant  sections  of  small  encrinal  stems 
(fig.  1).  This  same  bed  at  one  place  yielded  two  orthoceras- 
like  specimens  (figs.  2  and  4)  which,  however,  it  is  hardly  pos- 
sible to  identify.  Some  of  the  rock  seen  on  surfaces  cutting 
across  the  bedding  is  distinctly  striped  in  appearance.  It  was 
at  this  locality  that  some  fragmentary  dolomitic  and  siliceous 
rocks,  very  limited  in  exposure,  were  noted.  They  bear  some 
resemblance  to  the  interbedded  members  of  the  Cambrian  farther 
east ;  but  from  observations  made  about  a  mile  farther  west 
where  more  extensive  siliceous  beds  seem  to  belong  with  a  series 
which  includes  also  the  striped  and  dove-colored  rocks,  their 
Cambrian  age  was  regarded  as  improbable.  The  fossiliferous 
rock  and  its  associates  are  regarded  as  probably  Chazy.  It 
seemed  likely  that  Maclurea  magna  might  be  found  but  a  care- 
ful search  did  not  reveal  it. 

Northwest  of  the  limited  exposures  just  described,  over  the 
hill,  across  a  road  and  down  a  northwestern  slope  to  a  brook, 
for  a  distance  of  about  a  mile  is  nothing  but  drift.  Just  west 
of  this  brook  and  north  of  the  road  to  Cold  Spring  Corner  are 
low-lying  ledges  of  black,  pyritiferous  phylHte.  This  rock  passes 
northward  beneath  greatly  jammed  and  distorted  limestone  in 
which  the  patchy,  dove-colored  rock  appears  again  in  association 


REPORT  OB'  THE  VERMONT  STATE  GEOLOGIST.  235 

with  gray  dolomite  beds,  which  are  infolded  and  otherwise  in- 
volved with  the  other  rock.  These  beds  of  hmestone  clearly  rest 
on  the  phyllite.  The  deformation  of  the  limestone  beds  is  very 
severe;  they  are  folded  and  overturned,  profoundly  sheared, 
jointed  and  mashed.  Fossils  have  not  escaped.  In  one  exposure 
only,  a  small  slab  about  6  feet  square,  and  perhaps  not  in  place, 
although  lithologically  resembling  some  of  the  ledges  and  quite 
like  some  rock  seen  a  mile  east,  showed  some  coils,  most  of  which 
'  were  thick  patches  but  clearly  fossils.  A  piece  of  this  slab  is 
shown  in  figure  3,  plate  XXXVII.  The  ledges  at  this  place  were 
similar  to  those  described  above  as  carrying  fossils. 

Westward  across  a  narrow  swamp,  in  some  woods  and  in 
the  field  north,  are  many  ledges  of  similar  rocks,  although  inter- 
bedded  quartzite  is  frequent  here.  These  rocks  have  resemblance 
to  some  that  were  noted  west  of  Brandon  just  east  of  the  Rutland 
R.  R.  track  on  both  sides  of  the  road  through  Morgan's  Stock 
Farm  and  also  to  some  others  on  the  strike  of  the  latter  on  the 
west  side  of  Otter  Creek  along  the  eastern  margin  of  Long 
Swamp ;  also  with  others  found  west  of  Orwell  village.  These 
latter  rocks  in  Shaftsbury  were  hard  to  correlate  with  others  of 
the  vicinity. 

The  suggestion  is  strong  from  the  field  relations  that  the 
phyllite  mentioned  above  lies  beneath  all  these  various  calcareous 
rocks  north  of  the  road  to  Cold  Spring  Corner. 

It  seems  probable  that  the  various  outcrops  of  dove-colored 
rocks  carrying  gray  patches  and  fossils,  and  the  associated  gray 
beds,  and  perhaps  also  those  with  the  interbedded  quartzite, 
belong  to  the  Chazy,  on  the  basis  of  similarity  with  the  outcrops 
south  of  Bennington  and  at  places  northward  in  the  State. 

An  especially  interesting  feature  of  the  exposures  in  Shafts- 
bury  described  above  is  the  subjacent  position  of  the  black  phyl- 
lite, in  view  of  relations  which  have  been  described  for  areas 
farther  north.  At  places  west  and  southwest  of  North  Ben- 
nington the  relations  between  limestone  and  schist  afiford  reasons 
for  thinking  that  the  limestone  rests  upon  the  schist  formation. 

On  the  lower  portion  of  the  southern  slope  of  West  Mountain 
are  calcareous  rocks  similar  to  those  just  described.  They  are 
greatly  sheared  and  "splintered."  Up  the  southeastern  slope  of 
the  mountain  the  limestone  gives  place  at  the  surface  to  phyllite. 
At  the  top  of  the  mountain  is  a  light-colored,  siliceous  phyllite 
very  similar  to  rock  found  associated  with  quartzite  and  black 
phyllite  in  the  Sudbury  hills  except  that  the  former  is  more 
micaceous  and  schistose. 

Summary  of  the  Bennington  region.  Both  the  rocks  and  the 
relations  which  they  have  to  each  other  in  this  region  show  many 
resemblances  to  those  which  have  been  described  for  the  region 
around  Brandon.  There  are  also  differences.  In  general  the 
Lower  Cambrian  series  along  the  east  side  of  the  valley,  in  its 


236  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

lithological  characters  and  its  structural  features,  much  resembles 
the  other  in  each  case.  At  Brandon  black,  and  often  pyritiferous, 
schist  is  associated  with  the  quartzite  along  the  plateau  margin. 
At  Bennington,  except  for  a  small  patch  lying  on  members  of  the 
interbedded  series  against  the  edge  of  the  plateau,  southeast  of 
Barber's  Pond,  and  the  schist  of  Mason  Hill,  phyllite  was  not 
noted  as  involved  with  quartzite  in  proximity  to  the  plateau.  But 
it  should  be  noted  that  much  of  the  rock  making  up  the  Mt. 
Anthony  ridge,  south  of  the  latitude  of  Carpenter  Hill  at  least, 
is  not  to  be  distinguished  from  that  found  along  the  plateau  east 
of  Brandon.  It  is  apparently  the  same  schist  which  is  found  in 
both  places  and  which  also  underlies  the  calcareous  rocks  de- 
scribed above  north  of  the  Cold  Spring  road  in  Shaftsbury.  This 
schist  has  a  marked  similarity  throughout  a  wide  distribution,  as 
has  been  l^rought  out  fully  above. 

A  section  south  of  Bennington,  in  Pownal,  from  the  plateau 
on  the  east  across  the  valley  and  the  Mt.  Anthony  schist  ridge, 
gives  gneiss  with  overlying  quartzite,  faulted  with  quartzite  and 
overlying  calcareous  rocks,  which  are  faulted  with  each  other. 
These  latter  rocks  apparently  extend  to  the  base  of  the  schist 
ridge  on  the  west  of  the  valley  and  here  now  apparently  are 
faulted  again  against  quartzite  and  phyllite  which  form  the  scarp 
and  the  surface  rock  along  the  eastern  portion  of  the  ridge. 
Farther  west  lies  the  limestone  of  North  Pownal  which  is  much 
involved  with  schist,  sometimes  intermingling  with  it  in  surface 
outcrops,  sometimes  underlying  it,  and  here  and  there  jammed  in 
with  it. 

Another  section  north  of  the  latter,  passing  through  Mt. 
Anthony  proper,  shows  sheared  and  brecciated  limestones,  some 
of  which  are  of  probable  Chazy  age,  lying  just  west  of  the  appar- 
ent western  edge  of  the  Lower  Cambrian  series  and  containing 
a  long  and  strongly-marked  zone  of  crushing,  as  well  as  the 
shearing  characteristic  of  the  whole  mass,  and  west  of  this  de- 
formed strip  gives  the  thick-bedded,  crystalline  marbles  of  Mt. 
Anthony  apparently  not  greatly  deformed  internally,  or  as  a  mass, 
and  overlain  by  schist  in  apparent  conformity. 

An  east-west  section  north  of  Bennington,  passing  just  south 
of  North  Bennington  village,  gives  the  Lower  Cambrian  as  before, 
then  an  interval  of  unknown  (drift-covered),  then  the  fiattish, 
dark  gray  limestones  of  Paran  Creek.  Farther  west  the  indica- 
tions are  that  limestone  rests  on  schist. 

A  section  passing  about  two  miles  north  of  North  Benning- 
ton gives  Lower  Cambrian  as  before,  an  interval  of  unknown, 
then  the  rocks  which  were  described  above  as  probable  Chazy 
and  others  associated  with  them.  These  at  places  lie  on  black, 
pyritiferous  phyllite  and  probably  are  over  much  of  the  area  now 
resting  on  the  phylhte. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  237 

Farther  north  still,.along  a  section  passing  through  Shafts- 
bury  Center  or  Shaftsbury  Depot  and  West  Mountain,  the  Lower 
Cambrian  series  Hes  on  the  east  side  of  the  valley,  then  certain 
limestones  near  the  foot  of  West  Mountain,  then  the  schist 
of  West  Mountain.  Except  for  one  small  patch  just  west  of 
Shaftsbury  Depot  along  the  lower  eastern  slope,  the  schist  of 
West  Mountain  was  not  found  to  have  any  limestone  resting  on 
it,  although  the  writer's  search  was  not  exhaustive. 

The  Lower  Cambrian  series  of  the  valley  is  clearly  a  dismem- 
bered part  of  a  mass  to  which  the  quartzite  of  the  plateau  also 
belonged ;  whether  the  result  of  reverse  or  normal  faulting  has 
already  been  discussed  for  its  northern  extension.  The  evidence 
in  this  Lower  Cambrian  series  shows  that  it  has  been  under  strong 
compressive  stress,  and  that  some  of  its  deformational  features 
are  due  to  such  stress.  The  conditions  exhibited  south  of  Ben- 
nington and  in  North  Pownal  show  the  action  of  powerful  com- 
pressive forces  in  the  region.  Some  rocks  seem  to  be  crushed 
more  than  others,  as  though  caught  and  confined  and  made  to 
deform  internally  because  they  could  not  get  away.  Other  rocks 
seem  to  have  escaped  great  internal  crushing  although  meta- 
morphosed by  other  processes,  such  as  recrystallization. 

The  apparent  minor  displacements  in  the  Lower  Cambrian 
series,  involving  overturned  folds  and  probable  reverse  faults, 
are  evidence  of  former  compression.  The  overturned  folding  in 
some  cases,  however,  may  have  been  due  to  friction  instead 
of  having  preceded  and  initiated  the  rupture.  In  the  Ben- 
nington region  the  evidence  of  upthrust  of  older  into  younger 
rocks  is  strong;  but  the  evidence  for  lateral  thrust,  or  better, 
lateral  movement,  is  not  so  apparent.  Farther  north,  marble 
that  is  almost  certainly  younger  in  age-  outcrops  from  beneath 
overthrust  Lower  Cambrian  rocks.  These  relations  were  not 
established  for  the  Bennington  area.  While  the  limestones  west 
of  North  Bennington  seem  to  be  thrust  on  schist  in  some  cases, 
and  have  undoubtedly  been  under  compression,  the  field  relations 
do  not  show  that  the  limestone  may  not  have  rested  on  the  ter- 
rigenous rocks  prior  to  the  deformation  of  the  former. 

In  the  writer's  first  description  of  the  geology  of  Bennington, 
the  character  of  the  Vermont  valley  as  primarily  a  structural 
valley  was  recognized ;  but  the  break  between  the  plateau  and  the 
valley  was  regarded  as  primarily  a  reverse  fault  and  the  normal 
displacement  producing  the  present  relations  was  thought  to  have 
utilized  the  earlier  reverse  fault  plane.  This  does  not  seem  likely 
from  the  relations  shown  in  other  areas. 

The  present  lateral  distribution  of  the  calcareous  members  of 
the  Lower  Cambrian  series  in  the  valley  has  no  necessary  rela- 
tion to  their  original  extension  eastward  or  westward.  Such 
extension  must  be  decided  by  other  considerations.  The  prob- 
ability of  primary  upthrust  of   Lower  Cambrian  and  of   later 


238  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

normal  faulting  of  a  part  of  the  series,  together  with  the  fact  of 
erosion,  calls  for  an  original  extension  of  the  Lower  Cambrian 
series  as  a  whole  to  the  eastward.  Whether  they  extend  west- 
ward at  depth  is  perhaps  another  question.  Whether  they  ever 
had  a  great  westward  extension  by  thrust  is  certainly  an  inde- 
pendent consideration. 

Certain  other  matters  may  be  postponed  until  the  general 
summary  for  western  Vermont  is  offered.  Enough  has  been  said 
to  show  that  the  relations  are  complex  and  that  one  is  practically 
driven  to  inspect  other  areas  to  obtain  light  on  this  one. 

ADDISON   COUNTY. 
Whiting  and  Shoreham  Townships. 

(Brandon  and  Ticonderoga  topographic  sheets.) 

Topography.  These  townships  lie  just  north  of  the  Taconic 
hills  of  Sudbury  and  Orwell,  in  the  southern  part  of  the  Cham- 
plain  lowland.  The  surface  is  low  for  the  most  part  in  Whiting ; 
the  eastern  boundary  of  the  township  in  fact  for  a  distance  of 
four  miles  is  Otter  Creek.  In  Shoreham  there  are  a  few  low 
hills. 

General  observations  in  Whiting  and  Shoreham.  There  has 
been  a  much  more  extensive  preservation  of  the  limestone  strata, 
which  have  been  noted  in  fragmentary  areas  in  Orwell,  Benson, 
Sudbury  and  elsewhere,  northward  in  the  portion  of  the  Cham- 
plain  lowland  extending  through  Whiting,  Shoreham  and  neigh- 
boring townships.  On  this  account,  some  of  the  relations  and 
the  ages  of  the  various  rocks  were  early  worked  out  in  these 
areas,  first  through  the  work  of  Wing  and  later  that  of  Brainerd 
and  Seely.  In  the  town  of  Shoreham  was  established  the  type 
section  of  the  Beekmantown  of  western  Vermont. 

In  the  course  of  his  studies  the  writer  reviewed  some  of  the 
field  relations  in  Whiting  and  Shoreham. 

The  phyllites  north  of  Sudbury  village  at  and  around  Web- 
ster corner,  which  have  already  been  described,  were  followed 
northward  along  the  road  to  Whiting  village  by  frequent  out- 
crops nearly  to  the  village.  Along  the  road  running  west  two 
miles  north  of  the  village  the  same  phyllites  were  traced  from 
the  school  house  on  the  Middlebury  road  past  Hitchcock's  resi- 
dence to  school  house  corner.  In  the  valley  of  the  brook  one- 
fourth  of  a  mile  west  of  Hitchcock's  place,  the  phyllite  forma- 
tion showed  patches  of  quartzite  with  vein  quartz  like  that  on 
Government  Hill  in  Sudbury  and  at  other  places  in  the  Sudbury 
hills.  In  general  no  essential  difiference  could  be  discerned  be- 
tween the  rocks  composing  the  low  ridge  which  extends  north- 
ward from  Sudbury  into  Whiting  and  those  which  make  up  the 
hills  of  Sudbury,  Orwell  and  Benson. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST,  239 

West  of  the  phyllite  formation  in  Whiting  just  described, 
the  section  described  by  Brainerd  and  Seely  for  eastern  Shore- 
ham  can  be  fairly  easily  followed  if  side  excursions  are  made 
frequently  enough  to  get  exposures  of  beds  which  are  soil-covered 
at  other  places  along  the  strike.  The  apparent  monoclinal  char- 
acter with  easterly  dip  and  the  apparent  thickness  as  described, 
can  be  made  out  and  duly  appreciated. 

One-third  of  a  mile  west  of  school  house  corner,  mentioned 
above,  the  road  which  goes  westerly  past  Hitchcock's  place  turns 
sharply  to  the  south  to  join  the  main  road  from  Whiting  village 
to  Shoreham  village.  Along  and  east  of  this  road  leading  south 
are  exposures  of  the  blue  Trenton  limestone  dipping  easterly 
at  an  angle  of  about  40°  and  extending  along  the  strike  practically 
north  and  south.  West  of  the  road  are  ledges  of  the  Chazy  and 
others  which  have  many  similarities  to  the  Chazy,  but  which 
Brainerd  and  Seely  called  division  E  of  their  Beekmantown. 
Along  another  road  just  west  appears  division  D  with  many  fos- 
sils at  numerous  places.  Then  follow  divisions  C,  B  and  A 
westward  over  Cutting  Hill  towards  Richville.  Just  east  of 
Richville  is  exposed  with  easterly  dip  along  the  main  road  the 
whitish,  quartzitic  sandstone  which  was  called  the  "Potsdam," 
and  which  is  described  as  forming  the  base  of  the  section. 

At  the  bridge  at  Richville,  east  of  the  road  and  in  the  river 
bank,  and  northward  the  rocks  show  great  confusion,  and  north 
of  Richville  at  places  beds  belonging  to  division  D  show  westerly 
dip  just  west  of  this  zone  of  disturbance.  As  recognized  and 
shown  by  Brainerd  and  Seely  a  fault  or  thrust  has  elevated  the 
"Potsdam"  against  younger  beds. 

West  of  Richville  the  "Potsdam"  outcrops  again  along  the 
road  to  Shoreham,  apparently  along  the  axis  of  a  ruptured  anti- 
clinal buckle  for  the  sandstone  apparently  rests  at  the  west 
against  division  C,  and  possibly  D,  This  broken  anticline,  how- 
ever, seems  to  belong  to  a  larger  mass  of  beds  which  has  ridden 
westward  along  a  deeper  and  more  extensive  thrust  plane,  cut- 
ting through  the  Beekmantown  and  still  higher  beds.  Just  east 
of  Shoreham  village,  near  and  east  of  the  Catholic  Church,  are 
Trenton  rocks  succeeded  eastward  by  Chazy  beds  dipping  west- 
erly, which  in  turn  are  succeeded  eastward  by  Upper  Beekman- 
town, dipping  at  a  high  angle  easterly,  according  to  the  writer's 
observations.  It  would  seem  that  beds  which  stood  at  a  high 
angle  of  westerly  dip  at  the  time  of  rupture  would  have  had  this 
increased  and  even  reversed  by  the  drag  along  a  thrust  plane. 

In  the  center  of  the  village  the  "Potsdam"  appears  again 
on  the  eastern  margin  of  an  extensive  swamp  which  westward 
is  succeeded  by  hills  of  "Utica"  slates. 

South  of  Shoreham  in  the  town  of  Orwell,  field  relations 
which  have  been  described  above,  indicate  that  a  limestone  series 
like  that  which  occurs  in  Shoreham  has  been  broken  by  reverse 


240  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

faulting  and  minor  thrusting  which  have  brought  the  lower  mem- 
bers of  the  series  against  and  over  higher  ones,  and  that  as  now 
affected  by  erosion  at  some  places  the  younger  rocks  are  shown 
beneath  and  the  older  on  top.  Moreover,  other  more  extensive 
thrust  planes  have  carried  the  previously  faulted  series  over  still 
younger  rocks  on  which  it  may  now  be  seen  resting  at  several 
places. 

From  the  description  of  the  relations  as  inspected  in  Whiting 
and  Shoreham  the  similarity  to  the  condition  in  Orwell  appears. 
The  same  phyllites  occur  at  the  east  succeeded  westward  by  an 
unusually  regular  series  of  calcareous  rocks  from  the  Trenton 
down  through  the  gray  sandstone  called  the  "Potsdam,"  while 
still  farther  west  near  the  lake  are  hills  of  "Utica"  slate.  Except 
as  affected  by  erosion  the  arrangement  and  sequence  are  ap- 
parently the  same  and  it  would  seem  that  the  structural  relations 
of  both  areas  must  have  been  due  to  similar  causes. 

The  conditions  in  western  Shoreham  and  western  Orwell 
townships  raise  two  questions  : 

1.  How  is  the  preservation  of  the  hills  of  rather  frail 
"Utica"  shales  and  included  limestone  bands  along  the  edge  of 
the  lake  to  be  explained  unless  by  assuming  their  protection  per- 
haps until  relatively  recent  times  by  a  more  durable  covering? 

2.  What  explanation  is  to  be  given  of  the  absence  at  the 
west  of  the  phyllite  formation  found  at  the  east  beneath  the  lime- 
stones ? 

ADDISON   COUTfTY. 

Townships   of   Leicester,   Salisbury,   Middlebury,   Cornwall,   Bridport, 
Weybridge,  Addison,  IVew  Haren,  Walthara  and  Tergennes. 

(Brandon,  Ticonderoga,  Port  Henry  and  Middlebury  topographic 

sheets.) 

Topography.  The  topography  of  the  areas  examined  in 
these  townships  is  for  the  most  part  typical  of  the  Champlain 
lowland.  Snake  and  Buck  mountains  are  somewhat  conspicuous 
elevations  whose  structural  significance  will  be  discussed  beyond. 

Observations  between  Lake  Dunmore  and  Snake  Mountain. 
In  the  summer  of  1918  two  days  were  spent  in  as  careful  an  ex- 
amination as  a  walking  trip  would  permit  of  the  country  between 
Brandon  village  and  Vergennes.  The  first  part  of  the  trip  was 
along  an  irregular  traverse  from  Brandon  by  way  of  Lake  Dun- 
more  to  Snake  Mountain  through  the  townships  of  Leicester, 
Salisbury,  Middlebury,  Cornwall  and  Weybridge. 

North  of  Forestdale  the  western  boundary  of  the  quartzite 
formation  swings  from  the  plateau  to  the  Champlain  lowland 
and  marks  the  beginning  of  a  westward  extension  of  this  forma- 
tion that  in  the  lowland  becomes  even  more  pronounced  at  the 
north  in  Monkton. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  241 

The  Structural  breaks  between  the  plateau  and  lowland  north 
of  Brandon  exhibit  their  own  peculiar  pattern,  but  in  it  can  be 
discerned  a  similarity  to  that  at  the  south,  m  the  overlapping  along 
the  strike  of  normal  fault  displacements  of  varying  throw.  North- 
ward the  western  margin  of  the  plateau  is  farther  west  than  it 
is  east  of  Brandon.  The  dismembered  portions  of  the  quartzite, 
or  rather  the  Lower  Cambrian  series,  along  the  eastern  margin 
of  the  lowland  take  the  form  of  hills  and  ridges  which  begin  west 
of  Lake  Dunmore  and  gain  in  prominence  northward.  In  gen- 
eral the  relations  are  similar  to  those  shown  along  the  eastern 
margin  of  the  Vermont  valley  from  Bennington,  through  Shafts- 
bury,  Arlington  and  farther  north.  Observations  were  not  made 
with  sufficient  thoroughness  to  show  conclusively  whether  or  not 
outcrops  of  marble,  or  the  rocks  associated  with  it,  occur  within 
the  area  chiefly  occupied  by  the  Lower  Cambrian  series,  and  there- 
fore whether  actual  overlap  occurs  as  it  does  around  Brandon, 
although  probable  overlap  by  thrust  is  suggested. 

Dolomite  like  that  associated  with  the  marble  around  Bran- 
don and  farther  south  in  Dorset  was  noted  at  Leicester  Junction 
and  at  other  places  and  the  interbedded  series  was  found  a  mile 
west  of  East  Middlebury  village  along  the  road  from  that  village 
to  Middlebury.  The  valley  quartzite,  however,  northwest  of  Lake 
Dunmore  extends  westward  to  a  meridian  a  mile  west  of  East 
Middlebury  village,  at  least. 

East  of  Lake  Dunmore  is  a  prominent  scarp  in  the  quartzite 
and  the  lake  appears  to  lie  in  a  structural  basin.  North  of  Lake 
Dunmore  the  place  of  this  scarp  is  taken  by  another  lower  one 
which  breaks  the  quartzite  a  mile  west  of  Bryant  Mountain.  The 
basin  in  which  the  lake  Hes  appears  to  be  the  counterpart  of  those 
at  the  south  near  Arlington  and  Manchester  which  are  filled  with 
drift. 

Three  miles  northwest  of  East  Middlebury  village,  and  two 
miles  from  outcrops  of  the  interbedded  rocks  of  the  Lower  Cam- 
brian series  west  of  the  village,  along  the  road  to  Middlebury,  are 
exposures  of  sheared,  blue  limestone,  carrying  gray,  woolly 
patches  which  after  a  short  distance  are  succeeded  by  outcrops 
of  marble  that  lie  about  a  mile  southeast  of  Middlebury  village. 
The  relations  thus  far  noted  present  a  strong  similarity  to  those 
found  around  Brandon. 

In  the  fields  a  mile  west  of  Middlebury  are  abundant  expo- 
sures of  the  bluish  or  dove-colored  rock  showing  the  same  shear- 
ing and  the  same  gray  patches  that  have  so  frequently  been  men- 
tioned and  which  are  associated  with  other  limestones  resembling 
the  Trenton.  Many  ledges  were  examined  for  fossils,  but  nothing 
definite  was  noted.  The  prominent  structural  feature  is  strong 
shearing  with  easterly  dip. 

Two  miles  west  of  Middlebury  were  observed  outcrops  of 
phyllite.     Some  of  this  rock  is  like  the  light-colored  phyllites  seen 


242  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

in  the  Whiting  and  Sudbury  exposures,  in  texture,  but  darker  in 
color.  It  was  found  along  the  valley  of  Ledge  Creek.  No  at- 
tempt was  made  to  trace  the  boundaries  of  this  formation  with 
adjacent  rocks  and  no  contacts  were  found. 

West  of  the  phyllite  is  a  ridge  known  as  "The  Ledge."  The 
dove-colored  rock  was  noted  here.  West  of  "The  Ledge"  the 
surface  sinks  to  the  level  of  the  Lemon  Fair  River  in  Weybridge. 
West  of  the  Fair  the  surface  rises  very  gradually  to  the  eastern 
slope  of  Snake  Mountain. 

Observations  near  Snake  and  Buck  mountains.  In  the  north- 
eastern part  of  Bridport  the  eastern  slope  of  Snake  Mountain  is 
formed  of  cherry-red  or  brick-red  quartzite  which  dips  easterly. 
On  the  west  the  mountain  presents  a  good  scarp  of  varying  alti- 
tude fronting  the  lowland,  but  at  places  the  drift  is  piled  rather 
high  against  it. 

Along  and  near  the  east  road  to  Addison,  west  of  the  moun- 
tain, are  good  exposures  of  the' grayish-blue  limestone  carrying 
Maclureas,  Ophiletas  and  other  fossils. 

Two  miles  east  of  Addison  village,  along  the  road  to  New 
Haven  Junction,  north  of  the  mountain,  were  noted  black  shales, 
weathering  gray,  and  these  one-half  mile  farther  east  in  an  ex- 
cavation beside  the  road  one-half  mile  west  of  Otter  Creek  gave 
many  graptolites,  identified  as  G.  pristis.  Above  the  shales  in 
this  pit  is  limestone  apparently  lying  on  the  shales  and  which  in 
lithology  resembles  some  of  the  higher  Beekmantown.  At  the 
bridge  across  Otter  Creek  is  dove-colored  limestone  which  ap- 
pears again  northward  along  the  road  to  Vergennes  apparently 
dipping  easterly.  Farther  north,  three  and  a  half  miles  south  of 
Vergennes,  the  limestone  dips  easterly  about  20°  and  is  full  of 
fossils,  including  Maclurea  magna.  The  rock  does  not  appear 
to  be  so  badly  sheared  as  is  its  apparent  counterpart  east  of  Snake 
Mountain  and  southeast  of  Middlebury. 

Buck  Mountain  shows  a  conspicuous  scarp  on  the  west  which 
is  not  so  sharp  as  that  of  Snake  Mountain. 

East  of  the  limestone  at  the  bridge  over  Otter  Creek,  along 
the  road  from  Addison  village  to  New  Haven  Junction,  limestone 
gives  place  to  quartzite,  "Red  Sandrock,"  which  forms  the  east- 
ern slope  of  Buck  Mountain  and  dips  easterly.  This  gives  place 
eastward  to  limestone. 

Near  the  northern  end  of  Buck  Mountain  a  road  crosses  it. 
North  of  this  road,  quartzite  forms  the  base  of  the  eastern  slope, 
but  a  short  distance  west  up  the  slope  it  gives  place  to  large  ex- 
posures of  the  bluish  or  dove-colored  rock  with  its  gray  associate 
and  the  former  carries  indistinct  fossils.  Field  notes  indicate 
that  the  limestone  is  sheared  and  that  it  continues  westerly  and 
apparently  forms  an  anticline,  for  easterly  dip  occurs  on  the 
east  and  one-fourth  of  a  mile  west  the  dip  is  westerly.  North- 
ward along  the  strike  of  the  westerly  dip  the  lirnestone  presents 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  243 

an  abrupt,  abraded  edge  500  yards  south  of  the  house  at  the  end 
of  the  private  road.  About  three-fourths  of  a  mile  farther 
north  and  one  mile  south  of  Vergennes,  in  a  pit  east  of  the  road, 
shale  appears.  Here  the  rock  has  a  larger  exposure  and  is  more 
limy  than  that  noted  farther  south,  north  of  Snake  Mountain, 
but  in  general  resembles  that  in  which  graptolites  were  found 
two  and  a  half  miles  east  of  Addison  village.  The  shales  appear 
on  a  meridian  intermediate  between  limestone  outcrops  farther 
south  which  suggests  that  they  were  once  covered  by  limestone 
or  quartzite  which  has  been  eroded.  In  the  south  wall  of  the 
pit  the  rocks  show  that  the  formation  has  been  greatly  crumpled. 

Summary.  The  faulted  and  scarped  western  edge  of  the 
Green  Mountain  plateau  continues  northward  from  Brandon  and 
fronts  a  wide  Champlain  lowland  lying  to  the  west.  Along  the 
eastern  margin  of  the  lowland  lies  a  series  of  rocks  whose  basal 
quartzite  member  is  like  the  quartzite  forming  the  escarpments 
of  the  plateau.  In  the  lowland  and  on  the  edge  of  the  plateau 
the  quartzite  is  overlain  by  a  dolomite  and  in  the  lowland  there 
is  present  also  a  series  of  interbedded  dolomitic  and  quartzitic 
rocks  like  those  that  have  been  described  for  Brandon  and  areas 
farther  south.  The  lowland  rocks  are  dismembered  portions  of 
those  forming  the  plateau.  The  relations  in  the  main  are  like 
those  at  the  south  throughout  the  long  extent  through  which 
they  have  been  traced  in  the  descriptions  of  this  paper. 

Although  conclusive  evidence  from  field  relations  examined 
by  the  writer  may  not  be  offered  to  show  that  the  Lower  Cam- 
brian series  at  the  east  overlaps  other  rocks  along  a  thrust  plane, 
such  as  was  described  for  Brandon,  a  dolomite  was  seen  during  a 
subsequent  season  at  Leicester  Junction,  lying  on  the  marble,  and 
the  resemblance  of  the  former  to  the  dolomites  so  frequently 
noted  around  Brandon  in  association  with  the  marble  was  noted. 
It  does  not  resemble  the  rocks  which  seem  to  be  Chazy  and  its 
counterpart  was  not  found  west  of  the  meridian  of  Middlebury 
village.  During  a  subsequent  season  also  were  inspected  some 
outcrops  along  the  road  from  Leicester  Junction  to  Whiting 
village  which  bear  strong  resemblance  to  the  interbedded  rocks 
seen  northwest  of  Brandon  village.  They  occur  south  of  the 
road  about  a  mile  west  of  the  Junction  and  the  exposure  is  limited. 
In  fact,  drift  very  thoroughly  hides  the  hard  rock  between  Otter 
Creek  and  the  brook  farther  west,  and  the  exposures  are  not  at 
all  satisfactory  for  study.  Two  and  a  half  miles  west  of  the 
Junction,  just  east  of  the  railroad  track,  limestone  shows  a  pud- 
dled appearance  and  carries  salmon-pink  or  buff-yellow  patches 
of  calcite  like  those  northwest  of  Brandon.  In  Huntley's  quarry 
at  the  Junction  a  dolomite  is  involved  with  pinkish  marble  and 
west  of  the  quarry,  at  some  old  quarry  holes,  beds  of  ochre-yellow 
dolomite  are  involved  with  pinkish  marble. 


244  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

South  of  the  Leicester  Junction-Whiting  road  some  of  the 
few  exposures  along  the  road  to  Foster  corner  show  the  sheared 
blue  limestone  of  the  Sudbury  exposures  farther  south. 

If  the  various  outcrops  indicated  above  belong  to  the  Lower 
Cambrian  series  they  carry  the  margin  of  it  west  of  the  meridians 
along  which  the  marble  and  its  associated  rocks  outcrop  at  Leices- 
ter Junction,  and  southeast  and  northeast  of  Middlebury  village. 

At  Swinington's  quarry  near  Leicester  Junction  the  dolomite 
shows  a  structure  like  that  at  the  old  Norcross  quarry  at  South 
Dorset.  They  both  offer  structure  to  be  considered  in  connection 
with  the  characteristic  deformations  of  the  rocks  of  the  region. 
See  plate  XXXV. 

The  bluish-gray  or ,  dove-colored  limestone  and  associated 
gray  dolomite  southeast  and  west  of  Middlebury  village  are  re- 
garded as  the  equivalents  of  similar  rocks  around  Brandon  and 
west  of  it.  West  of  Middlebury  they  have  apparently  the  same 
relations  to  sheared  blue  limestone  as  in  eastern  Sudbury  and 
the  whole  series  bears  the  same  relation  to  the  phyllite  in  eastern 
Cornwall  that  the  calcareous  rocks  at  the  south  do  to  the  phyllite 
formation  of  the  Sudbury  and  Orwell  hills.  In  eastern  Corn- 
wall, in  fact,  the  phyllite  band  simply  interrupts  at  the  present 
surface  the  continuity  of  entirely  similar  calcareous  rocks  that 
now  lie  each  side  of  it.  These  calcareous  rocks  lie  on  the  phyllite 
and  are  not  interbedded  with  it.  Westward  in  the  valley  of  the 
Lemon  Fair  the  hard  rocks  largely  or  wholly  disappear  from 
surface  view  and  the  next  outcrops  westward  are  the  quartzitic 
rocks  of  the  "Red  Sandrock"  formation  on  the  eastern  slopes  of 
Snake  Mountain.  Farther  north,  however,  on  the  meridians  of 
the  phyllite  and  the  limestones  west  of  Middlebury  the  "Red  Sand- 
rock"  of  Buck  Mountain  appears  at  the  surface  with  every  in- 
dication at  its  northern  end  that  limestones  similar  to  those  lying 
on  the  phyllite  west  of  Middlebury  village  also  lie  on  it,  while  the 
quartzite  on  the  eastern  slope  of  Buck  Mountain  passes  eastward 
beneath  similar  limestones.  Whatever  it  may  mean,  there  is  a 
substratum  to  these  similar  limestones  which  shows  a  lateral 
variation  within  not  very  long  distances  from  phyllite  to  quartzite. 

The  published  descriptions  show  that  with  minor  surface  in- 
terruptions the  quartzite  of  Buck  Mountain  connects  northeast- 
erly with  similar  rock  in  Monkton,  which  in  turn  is  described  as 
"merging"  with  the  quartzite  of  the  plateau.  Account  should 
be  taken,  of  course,  of  the  normal  and  other  probable  displace- 
ments at  the  east. 

Snake  and  Buck  mountains  are  the  topographic  counterparts 
of  the  interbedded  quartzite  and  phyllites  composing  the  Orwell 
hills.     They  also  lie  along  practically  the  same  meridian. 

West  of  Snake  Mountain  are  calcareous  rocks  apparently 
similar  in  important  respects  to  those  at  the  east,  but  less  altered, 
and   fossiliferous;   the  dove-colored   rocks   yield   Chazy   fossils. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  245 

North  of  Snake  Mountain  are  black  shales  giving  "Utica"  grapto- 
lites  and  this  rock  is  overlain  by  limestone,  which  is  probably 
of  Beekmantown  or  Chazy  age.  Along  a  meridian  lying  a  mile 
to  the  east  are  dove-colored  rocks  which  northward  west  "~of 
Buck  Mountain  give  Maclurea  magna  and  other  Chazy  fossils. 
And  still  farther  north  and  on  a  meridian  lying  east  of  the  Chazy 
outcrops  are  shales  like  those  at  the  south  carrying  Graptolithus 
pristis. 

There  is  apparently  a  fault  in  the  quartzite  on  the  north  of 
Snake  Mountain,  but  it  is  not  apparent  that  there  is  any  structural 
lateral  offset.  The  physiographic  offset  between  Snake  and  Buck 
mountains  appears  to  be  due  to  the  irregular  course  of  the  dis- 
placement that  bounds  those  eminences  on  the  west  and  which 
north  of  Snake  Mountain  swings  eastward  and  then  again  north- 
ward. There  are  minor  scarps  and  surface  interruptions  between 
Snake  and  Buck  mountains.  Around  Snake  and  Buck  mountains 
there  were  not  noted  by  the  writer  any  places  at  which  the  quartz- 
ite and  shales  are  in  contact  and  only  one  place,  as  described,  was 
seen  where  the  shales  had  limestone  above  them.  The  probable 
relations  of  the  quartzite,  and  the  limestone  which  probably  lies 
on  it,  to  the  "Utica"  rest  upon  probable  conditions  shown  else- 
where which  will  be  described  beyond. 

The  displacements  marked  by  the  scarps  on  the  west  of 
Snake  and  Buck  mountains  have  been  described  or  pictured  as 
reverse  faults  by  which  the  quartzite  was  elevated  to  its  present 
position  with  respect  to  the  surrounding  rocks.  They  will  be 
discussed  beyond  so  as  to  show  that  they  are  probably  in  char- 
acter, and  relations  to  earlier  thrusts,  similar  to  those  which  broke 
the  rocks  along  the  western  edge  of  the  plateau  at  the  east  and 
the  Orwell  and  Benson  hills  at  the  south. 

CHITTENDEIf  COTI\W. 

Burlington. 

(Burlington  topographic  sheet.) 

Observations  near  Burlington.  Vergennes  was  the  most 
northern  point  reached  by  the  writer  in  the  course  of  a  trip  on 
foot  through  western  Vermont  in  the  summer  of  1918.  There 
has  been  no  opportunity  since  to  make  close  field  observations 
between  the  parallels  of  Vergennes  and  Burlington.  Some  men- 
tion may  be  made  in  the  final  summary  of  certain  published  ac- 
counts of  the  relations  shown  in  the  territory  intervening.  At 
Burlington  trips  were  made  to  points  along  the  lake  shore  and  to 
the  valley  of  the  Winooski,  which  may  be  mentioned  here  for 
sake  of  completeness. 

The  celebrated  Rock  Point  locality  at  Burlington  should  be 
visited  by  anyone  who  is  interested  in  the  problems  of  rock 
deformation  in  western  Vermont.     Here  is  exposed  a  relation 


246  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

that  is  often  concealed  along  the  lake  shore.  The  phenomenon 
of  overthrust  falls  within  the  range  of  easy  understanding  as 
one  surveys  the  sharp  contact  of  the  Cambrian  sandstone  on  the 
Ordovician  shale  formation,  and  the  inspection  is  helpful  in 
visualizing  the  relations  at  other  places  where  the  aid  of  the 
imagination  is  needed  more. 

The  massive  quartzite-dolomite,  "Red  Sandrock,"  often  with- 
out any  marked  visible  internal  deformation,  rests  on  greatly 
crushed  and  crumpled,  black  slates  and  shales,  with  stringers  and 
nests  of  quartz  and  calcite.  The  color  of  the  quartzite  varies  in 
this  vicinity ;  while  often  red  it  is  frequently  gray  and  brown. 
The  shore  section  at  Rock  Point  is  a  detached  one ;  north  and 
south  of  it  the  shore  is  in  Champlain  clays. 

East  of  the  lake  shore  the  best  exposures  near  Burlington 
are  along  the  Winooski  River.  At  the  Lower  Falls,  red  and  gray 
quartzite  in  massive  ledges  in  the  stream  and  along  the  banks  lie 
in  a  flattish  position,  dipping  gently  in  a  general  easterly  or 
jiortheasterly  direction.  East  of  Winooski  village  the  gray 
quartzite  is  succeeded  by  limestone  of  uncertain  age. 

FEANKLIN  COUNTY. 
St.  Albans  Bay. 

(St.  Albans  and  Milton  topographic  sheets.) 

Some  observations  along  the  lake  shore  south  of  St.  Albans 
Bay.  Some  apology  seems  necessary  for  the  very  brief  original 
notes  offered  for  the  country  north  of  Burlington.  A  part  of 
one  rainy  day  was  spent  along  the  lake  shore  near  St.  Albans 
Bay  south  of  Melville  Landing.  Heavy  weather  prevented  much 
being  done  on  the  trip  and  illness  from  influenza  practically  closed 
field  work  for  the  season. 

From  Melville  Landing  southward  the  shore  as  followed  for 
three  miles  towards  Camp  Rich  in  Milton  is  formed  of  "Utica" 
slates  and  shales  which  form  low  cliffs  and  minor  headlands. 
The  road  hugs  the  shore  for  the  distance  mentioned  and  advan- 
tage has  evidently  been  taken  of  the  level  topography  in  laying 
the  road  out.  Back  from  the  shore  at  varying  distances  &re  ex- 
posures of  limestone  which  were  not  examined  except  as  men- 
tioned beyond.  The  slates  were  inspected  casually  for  fossils 
but  none  was  found. 

About  two  miles  north  of  Camp  Rich,  above  a  shore  clifif  of 
the  shale  and  only  a  few  rods  from  the  shore,  were  noted  light- 
colored,  siliceous  phyllites  or  slates  which  at  once  recalled  the 
similar  rocks  in  Whiting  and  Sudbury.  This  exposure  seemed 
somewhat  isolated  and  surrounded  landward  by  limestone. 
Ledges  of  the  latter  occur  only  a  few  feet  away  from  the  slate, 
but  the  contact  was  not  seen.  The  relations  were  not  absolutely 
conclusive  as  to  whether  the  limestone  or  the  slate  was  superior 


REPORT  OP  THE3  VERMONT  STATE  GEOLOGIST.  247 

in  position.  The  shore  road  is  here  a  fourth  of  a  mile  from  the 
bank.  Limestone  apparently  continues  eastward  to  the  road  and 
across  it.  East  of  the  road  a  low  ridge  of  gray,  "marbly"  lime- 
stone is  succeeded  by  a  fairly  high  escarpment  of  gray  dolomite. 
From  the  general  relations  as  noted  here  and  northward,  east  of 
the  shore  road,  it  was  concluded  that  the  phyllite  is  beneath  the 
limestone  and  that  the  former  rests  on  the  "Utica."  The  phyllite 
is  correlated  in  the  writer's  mind  with  similar  ones  farther  south 
in  Addison  County  and  is  thought  of  as,  in  general,  equivalent  to 
the  quartzite  or  "Red  Sandrock"  which  farther  south  in  Milton 
and  Colchester  comes  to  the  shore,  either  resting  on  the  "Utica" 
or  dipping  into  the  lake.  The  phyllite  north  of  Camp  Rich  as 
just  described  is  apparently  very  limited  as  a  surface  formation 
in  the  immediate  vicinity  of  the  outcrops  noted.  Northward 
towards  St.  Albans  Bay,  limestone  apparently  rests  on  the 
"Utica,"  to  judge  by  general  field  relations ;  but  both  phyllite  and 
limestone  are  regarded  as  resting  by  thrust  on  the  "Utica"  forma- 
tion. 

GRAND  ISLE  COUNTY. 
South  Hero  and  Grand  Isle. 

(Plattsburg  topographic  sheet.) 

During  the  season  of  1920  some  examination  was  made  of 
the  formations  on  the  island  of  Grand  Isle,  often  in  the  company 
of  the  State  Geologist.  The  geology  of  this  interesting  island 
has  been  most  recently  studied  by  Professor  Perkins,  whose  ex- 
cellent and  careful  descriptions  will  be  found  in  his  Second  and 
Third  Reports.  In  this  paper  the  writer  wishes  to  record  only  a 
few  observations  which  bear  more  particularly  upon  the  deforma- 
tion of  the  rocks. 

The  surface  mantle  on  the  rocks  of  Grand  Isle  is  largely  com- 
posed of  the  deposits  of  an  old  "lake"  bottom.  The  exposures  of 
the  hard  rocks,  however,  are  sufficiently  numerous  inland,  even 
over  the  lowest  portions,  to  permit  an  apparently  fairly  accurate 
delineation  of  the  boundaries  of  the  different  formations ;  but 
the  covering  is  heavy  enough  to  conceal  in  most  places  such 
critical  features  as  contacts  over  considerable  distances. 

In  a  general  way  the  formations  may  be  divided  into  the 
shale  formation,  which  occupies  the  northern,  eastern  and  south- 
eastern portions  of  the  island,  and  the  limestone  strata  which 
stretch  as  a  wide  strip  along  the  western  side  from  its  south- 
western end  northward  two-thirds  the  distance  across  the  island 
from  south  to  north,  and  which  at  the  north  extend  towards  the 
east  into  the  central  portions.  The  present  apparent  surface 
distribution,  in  a  large  way,  of  the  rocks  just  mentioned,  in  itself 
appears  to  have  some  structural  meaning  which  apparently  could 
hardly  be  grasped  in  its  true  signification  from  the  study  of  this 


248  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

island  alone.  Especially  confusing  would  probably  be  a  close 
age  relation  of  some  of  the  members  of  the  shale-slate  formation 
with  some  members  of  the  limestone  strata  and  an  apparent 
transition  between  the  two  at  many  places,  not  only  in  lithological 
characters,  but  in  the  fossils  as  well.  In  addition  to  these  features 
of  general  distribution  there  are  some  details  which  will  be  men- 
tioned presently. 

The  limestone  strata  include  the  Beekmantown,  as  a  small 
patch  at  the  southern  end,  which  is  better  exposed  on  Providence 
Island  a  mile  and  a  half  away,  the  Chazy,  Black  River  and  Tren- 
ton. In  general  as  seen  along  the  shore  and  also  inland  a  short 
way  from  it  the  beds  of  these  different  terranes  have  not  been 
greatly  deformed  internally.  An  almost  continuous  section  in 
limestone  extends  from  Phelps'  Point  at  the  southwest  to  Wilcox 
Cove  along  shore,  and  more  or  less  widely  interrupted  exposures 
occur  to  the  eastward  a  short  way  from  the  shore  along  an  old 
"lake"  bottom  and  along  the  old  beach  and  some  ridges  that  bound 
it  on  the  east. 

The  Chazy  rocks  are  usually  impressive  in  their  massive- 
ness.  Some  of  the  beds  are  several  feet  thick ;  in  one  case  a 
bed  is  as  much  as  20  feet  through.  These  strata  are  prevailingly 
quite  flat  in  position  along  shore,  and  so  far  as  examined  are 
free  of  pronounced  internal  deformation,  although  they  show 
more  evidence  of  it  inland  so  far  as  the  more  limited  exposures 
permit  observation. 

The  Black  River  beds  are  limited.  They  too  are  somewhat 
massive,  but  less  so  than  the  Chazy  rocks.  They  might  be  con- 
sidered as  somewhat  intermediate  in  this  respect  between  the 
Chazy  and  the  Trenton.  Along  shore  these  beds  are  also  pre- 
vailingly almost  fiat  in  position.  They  are  very  smoothly  and 
symmetrically  jointed  as  a  rule.  An  occasional  outcrop  of  rock 
with  some  characters  of  the  Black  River,  but  much  crushed  and 
filled  with  veins  of  calcite,  occurs  near  the  west  shore ;  but  a  con- 
sideration of  general  relations  makes  it  seem  doubtful  if  such 
rock  is  in  place. 

By  far  the  larger  part  of  the  limestone  as  mapped  for  the 
present  surface  belongs  to  what  is  called  Trenton,  and  which 
probably  is  Trenton,  but  perhaps  not  all  there  is  on  the  island 
that  should  be  included  in  this  terrane.  Professor  Perkins  has 
been  impressed  with  the  Trenton  or  transitional  character  of 
some  members  of  the  shale-slate  formation  and  has  been  at 
work  on  the  problem  of  a  clearer  separation  of  the  Trenton 
from  the  so-called  "Utica"  of  the  island.  From  what  will  be 
indicated  beyond  it  may  appear  that  structural  features  among 
some  of  these  rocks  will  have  to  be  considered  in  working  out 
their  age  and  other  relations. 

The  Trenton  rocks  that  are  readily  recognized  and  have  been 
mapped  as  such  have,  like  the  Black  River  and  Chazy,  where 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  249 

they  occur  along  shore  a  nearly  horizontal  position.  A  fine  sec- 
tion is  exposed  from  Rockwell  Bay  northward,  in  which  there 
appears  to  be  only  gentle  but  variable  incHnation  of  the  beds. 
The  exposed  portion  of  the  stratum  is  composed  of  limestone 
beds  of  varying  thickness,  ranging  from  2  through  4  or  6  to  8  or 
10  inches  with  intercalated  shaly  layers.  The  rocks  in  their  dark 
gray  and  somewhat  monotonous  appearance  throughout  are  in 
contrast  with  the  dense  and  more  heavily-bedded  Black  River  and 
the  massive  and  often  more  distinctly  marked  Chazy. 

Deformation  of  the  Trenton  beds,  including  visible  shearing 
within  them,  is  found  in  the  shore  section  and  now  and  then  a 
small  fold  or  buckle  appears  which  sometimes  appears  to  be  asso- 
ciated with  a  fault  displacement.  In  one  case  the  latter  appeared 
to  be  a  tension  fault ;  at  another  place,  near  Wilcox  Cove,  there 
was  suggestion  of  thrusting  and  therefore  of  compression.  On 
the  whole,  however,  along  shore  there  is  less  evidence  within  the 
various  limestones  of  the  action  of  compressing  forces  upon  them 
than  farther  east.  There  is  some  evidence  of  norrnal  faulting 
across  the  general  strike  of  the  rocks,  both  within  formations  and 
between  them,  and  some  of  these  are  apparently  marked  by  shore 
indentations  at  the  present  time,  as  well  as  by  juxtaposition  of 
rocks  of  different  ages.  How  far  most  of  these  displacements 
may  run  inland  it  is  difficult  to  find  out. 

It  has  been  assumed  and  would  probably  by  many  observers 
be  assumed  that  these  various  limestone  beds  and  formations 
have  at  the  present  time  their  original  stratigraphic  interrelations 
and  primary  geological  sequence,  and  that  they  are  probably  near 
the  place  of  their  deposition ;  that,  in  other  words,  they  have  not 
been  greatly  disturbed  from  the  place  where  they  were  laid  down, 
though  bearing  some  evidence  of  deformation. 

The  careful  systematic  examination  which  would  be  neces- 
sary to  show  it  was  not  made  to  find  out  to  what  extent,  if  any, 
the  primary  interrelations  of  the  rocks  of  different  ages  which 
these  limestones  represent,  may  have  been  changed  by  the  action 
of  thrusts ;  but  in  addition  to  the  insignificant  disturbances  which 
have  been  mentioned,  effects  distinctly  to  be  attributed  to  the  ac- 
tion of  compression  were  observed  in  the  limestones  at  other 
places  on  the  island. 

Along  a  ridge  about  one-half-mile  east  of  the  west  shore  and 
east  of  Sawyer's  Bay,  and  eastward  from  this  ridge  in  more  scat- 
tered exposures,  beds  of  Trenton  limestone  give  satisfactory  evi- 
dence of  internal  deformation,  not  only  in  their  sheared  structure, 
but  in  the  compression,  distortion,  fragmentation,  or  obliteration 
of  their  fossils.  Minor  buckling  may  be  seen  and  an  easterly  dip 
due  to  shearing  can  be  readily  distinguished  from  that  of  strati- 
fication. Some  of  the  fragmentation  of  fossils  may  have  oc- 
curred during  or  prior  to  deposition ;  but  in  the  field  it  is  possible 
within  short  distances  across  the  strike,  and  sometimes  apparently 


250  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

along  the  strike,  to  pass  from  one  ledge  with  excellently  pre- 
served fossils,  such  as  Bellerophon,  to  other  ledges  in  which,  at 
the  distance  of  only  a  few  hundred  yards  at  the  most,  alteration 
will  vary  from  compression,  as  shown  by  a  flattened  Bellerophon, 
nearly  to  obliteration.  Account  is  taken  in  this  statement  of  dif- 
ferences in  fossil  contents  due  to  natural  variation  in  passing 
from  bed  to  bed  across  the  strike. 

Observations  seemed  to  indicate  that  in  the  Trenton  beds, 
because  of  their  more  thinly-bedded  character,  deformation  due 
to  buckling  and  crushing,  and  probably  shearing,  found  expres- 
sion more  readily  than  in  the  more  massive  Black  River  and 
Chazy.  It  hardly  needs  more  than  a  casual  inspection  of  the 
limestone  rocks  as  one  goes  east  from  the  lake  towards  their 
eastern  edge  to  discern  the  evidence  of  the  greater  disturbance 
and  deformation  which  they  show  over  those  along  the  lake  at 
the  west.  Along  their  eastern  margin  some  of  them  are  clearly 
crushed  and  carry  many  calcite  veins. 

The  limestone  formations  whose  deformational  features  have 
just  been  discussed  are  those  which  may  in  the  field  be  separated 
clearly  from  those  which  have  some  similar  lithologic  and  struc- 
tural characters,  but  which  are  in  more  intimate  major  structural 
association  with  the  shale-slate  formation.  Along  the  lake  shore  at 
places  between  Rockwell  Bay  and  Wilcox  Cove  beds  of  not  ap- 
preciably deformed  rocks  of  probable  Trenton  age  pass  into 
other  apparent  Trenton  rocks  which  are  rather  strongly  sheared, 
and  between  these  and  other  rocks  which  have  been  called  "Utica"^ 
there  is  sometimes  difficulty  in  drawing  any  decided  lithological 
distinction. 

The  so-called  "Utica"  slates  and  included  limestones,  perhaps 
together  with  some  Trenton  rocks,  may  apparently  as  a  forma- 
tion be  differentiated  somewhat  sharply  from  the  limestone  strata 
which  border  the  lake,  as  just  described,  on  the  basis  of  the  de- 
formation which  it  has  suffered.  In  general,  these  rocks  present 
much  the  same  aspect  with  respect  to  deformation  wherever  ob- 
served. Under  severe  compression  the  beds  of  the  shale-slate 
formation  have  not  only  been  folded  and  tilted,  but  apparently 
because  of  pronounced  difference  in  behavior  of  beds  of  different 
thickness  and  strength  under  stress  of  pressure  and  probably  also 
load,  there  has  been  frequent  rupture  with  much  crushing  and 
frequent  movement  of  one  part  of  the  mass  over  another  part, 
producing  great  confusion.  An  exposure  of  great  interest  as 
showing  this  behavior  of  the  slate  formation  is  to  be  seen  in  the 
cliffs  south  of  the  Grand  Isle  end  of  Sand  Bar  Bridge,  and  which 
is  pictured  in  the  Third  Report.  In  lithological  and  deforma- 
tional aspects  the  members  of  this  formation  are  like  those  along 
the  shore  of  the  mainland  south  of  St.  Albans  Bay  and  at  Burling- 
ton and  in  essentials  like  those  farther  south  in  Addison  County. 
The   lithological   differences   and   resemblances   among  the   dif- 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  251 

ferent  slates  and  shales  through  the  distances  separating  the 
localities  just  mentioned  are  of  the  same  order  and  character  as 
those  which  appear  in  comparing  the  slaies  of  western  Vermont 
with  those  of  some  parts  of  the  Hudson  valley. 

Interpretation.  In  the  course  of  the  writer's  examination 
of  Grand  Isle  the  question  arose  very  early  in  his  mind  as  to  what 
is  the  present  structural  relation  which  the  limestones  have  to  the 
slates.  Search  did  not  show  any  of  the  limestones  resting  on  the 
slates.  So  far  as  the  writer's  observations  have  gone,  and  also 
the  descriptions  of  others,  it  appears  that  the  structure  of  the 
island  as  a  whole  is  best  explained  by  the  relations  shown  at  the 
east  on  the  mainland  and  at  other  places  in  western  Vermont 
which  have  been  described  in  this  paper. 

In  the  first  place,  one  notes  the  relatively  great  deformation 
of  the  shale-slate  formation  already  referred  to  and  the  contrast 
which  it  bears  to  the  limestone  strata  viewed  as  a  mass.  The 
contrast  recalls  the  relations  on  the  mainland  where  a  dolomite- 
quartzite  showing  little  visible  internal  deformation  rests  on 
greatly  crumpled  slates  and  shales  in  all  essential  respects  like 
those  of  Grand  Isle  only  a  few  miles  to  the  west.  The  slates  of 
the  mainland  having  the  inferior  position  to  older  rocks  that  has 
been  noted  at  so  many  places,  but  in  this  connection,  especially 
along  the  lake  shore  from  St.  Albans  Bay  to  Burlington,  undoubt- 
edly once  had  connection  across  what  is  now  the  lake  surface 
between  the  mainland  and  Grand  Isle  with  the  slates  of  the  latter. 
Did  the  Cambrian  quartzite  ride  over  the  slates,  or  rather  did 
the  thrust  plane  along  which  it  was  driven  cut  through  the  slate 
formation  above  the  limestones  now  exposed  at  the  surface  on 
Grand  Isle,  or  did  it  cut  through  it  along  what  is  the  plane  of 
contact  of  these  limestones  on  the  slates?  In  other  words,  do 
the  limestones  of  Grand  Isle  structurally  lie  below  the  "Utica" 
of  the  island  or  above  it?  If  above  it,  they  he  unconformably 
along  a  thrust  plane  and  are  not  in  their  original  position.  The 
considerations  ofifered  all  suppose  the  slates  to  be  younger  than 
the  limestones.  On  such  a  supposition  as  overthrust  there  prob- 
ably will  not  be  in  most  cases,  of  course,  actual  transition  from 
undeformed  Trenton  limestone  into  deformed  "Utica"  slate  or 
limestone.  There  might,  however,  be  transition  from  sheared 
Trenton  limestone  into  continuous,  unsheared  limestone,  but  all 
within  the  mass  that  had  been  moved.  The  idea  of  overthrust 
does  not  preclude  the  inclusion  of  Trenton  rocks  in  the  "Utica," 
but  such  rocks  would  presumably  have  to  be  thought  of  as  having 
once  been  separated  from  the  undeformed  Trenton  rocks  by  a 
greater  or  less  interval. 

In  connection  with  the  idea  of  overthrust  the  question  of  the 
relations  of  the  limestone  strata  of  Grand  Isle  to  the  quartzite 
on  the  mainland  calls  for  consideration.  A  better  knowledge 
than  the  writer  has  of  what  lies  on  the  quartzite  east  of  the  lake 


252  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

might  help  in  answering  this  question.  Published  accounts  are 
not  conclusive.  Conditions  farther  south  that  have  been  exam- 
ined may  give  some  suggestions. 

Did  the  quartzite  which  now  lies  on  the  slate  formation  along 
the  mainland  at  Malletts  Bay  and  Burlington  once  extend  over 
both  the  slates  and  the  limestones  of  Grand  Isle?  Or  did  its  ex- 
tension westward  by  thrust  stop  short  of  Grand  Isle?  Its  ab- 
sence west  of  the  mainland  is  not  conclusive,  but  is  suggestive. 
It  would  seem  that  if  this  durable  formation  once  extended  any 
distance  west  of  the  eastern  shore  of  the  lake  some  remnant  of  it 
would  be  preserved.  In  this  connection  may  be  recalled  the  ap- 
parent contact  of  limestone  on  the  slates  around  St.  Albans  Bay 
with  apparently  no  quartzite  or  phyllite  intervening,  and  other 
places  southward  where  either  some  phyllite,  or  slate,  or  quartzite, 
lies  between  limestone  and  the  "Utica."  Again  may  be  noticed 
the  eastward  extension  of  the  lake  surface  to  form  St.  Albans 
Bay  where  apparently  only  limestone  rests  on  the  slate  formation. 
It  would  appear,  even  from  the  few  observations  made  by  the 
writer  in  northern  Vermont,  that  either  limestone,  or  quartzite, 
or  phyllite  may  rest  on  the  "Utica,"  presumably  by  thrust,  along 
the  mainland.  In  view  of  this  probability  it  is  not  difficult  to 
imagine  the  limestones  of  Grand  Isle  as  lying  on  the  slate-shale 
formation  by  thrust. 

In  the  areas  farther  south  that  have  been  described,  it  will  be 
recalled  that  along  the  lake  region  it  is  some  member  of  the  lime- 
stone that  lies  on  the  "Utica"  and  that  at  only  one  or  two  places 
of  obscure  relations  is  there  suggestion  of  visible  contact  of  any 
member  of  the  quartzite-phyllite  formation  on  terrigenous  rocks 
of  younger  age. 

The  correlation  and  unification  of  the  phenomena  of  these 
various  localities  will  have  to  be  undertaken  in  the  closing  sum- 
mary. 

At  places  on  Grand  Isle  the  Chazy  and  apparently  the  Black 
River  are  shown  to  have  such  relations  to  the  slates,  when  mapped 
and  when  inspected  in  the  field,  that  it  is  difficult  to  draw  any 
other  conclusion  than  that  the  two  are  in  contact.  At  other  places 
it  is  the  Trenton  that  is  or  appears  to  be  in  contact  with  the 
slates.  Judging  again  by  conditions  as  shown  farther  south, 
some  of  the  relations  of  limestone  to  slate  on  Grand  Isle  may  be 
the  results  of  displacements  due  to  normal  faulting;  but  all  of 
them  apparently  may  hardly  be  explained  on  such  a  basis.  There 
is  nothing  to  suggest  that  the  limestones  have  been  completely 
inverted ;  they  retain  at  least  their  depositional  attitude.  When 
one  finds  a  mass  of  Chazy  limestone  surrounded  on  three  sides 
by  the  slate  formation  and  remembers  that  the  latter  is  unques- 
tionably the  younger  rock,  two  possible  explanations  suggest  them- 
selves ;  either  younger  rock  has  simply  been  dropped  by  normal 
faulting  so  as  to  surround  the  older  rock,  partly  by  slates  perhaps 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  253 

and  partly  by  younger  Hmestone,  as  is  the  apparent  case  north  of 
Keeler  Bay ;  or  the  older  rock  has  been  thrust  on  the  younger 
strata.  The  first  hypothesis  is  entirely  adequate  to  explain  the 
present  relations,  if  perhaps  we  recognize  the  possibility  of  dif- 
ferential faulting,  for  there  is  apparently  nothing  in  the  interrela- 
tions of  the  different  limestone  strata  which  opposes  such  a  view. 
On  either  view  the  limestones  are  presumably  present  at  depth, 
but  in  one  case  the  limestones  are  different  at  depth  from  those 
at  the  surface  with  respect  to  their  original  relations  to  the  slates 
of  the  island  and  in  the  other  case  the  rocks  at  the  present  surface 
and  at  depth  have  presumably  simply  slipped  by  one  another  along 
planes  of  normal  faulting.  The  latter  view  would  of  course  have 
to  assume  some  disturbance  as  the  result  of  compression  in  order 
to  account  for  the  features  shown  by  the  various  rocks,  but  might 
in  the  minds  of  some,  not  appear  inconsistent  with  the  contrasts 
exhibited  by  the  two  principal  formations  of  the  island  with 
respect  to  their  deformation.  Such  a  view,  however,  does  not 
seem  to  take  sufficiently  into  account  the  obvious  thrust  deforma- 
tions of  the  region  of  which  the  island  is  a  part.  Whether  we 
assume  or  not  that  the  big  mass  of  Trenton  rocks  in  the  western 
part  of  the  island  is  underlain  by  Chazy  beds,  the  explanation  of 
relations  seems  to  be  possible  on  the  basis  of  thrusting.  Prob- 
ably we  should  have  to  take  into  account  that  the  map  to  show 
the  distribution  of  the  formations  is  not  absolutely  accurate, 
although  as  much  so  as  conditions  at  the  present  time  allow  in 
view  of  the  surface  covering  and  the  non-committal  or  doubtful 
character  of  isolated  and  small  outcrops.  Where  the  present 
conditions  suggest  Trenton  in  contact  with  slates  may  not  be 
really  the  case ;  but  even  if  it  should  be  normal  faulting  subse- 
quent to  other  deformation  might  readily  account  for  such  con- 
ditions, although  normal  faulting  is  perhaps  not  necessary  to 
explain  them. 

If  on  the  mainland  it  is  quartzite-dolomite  that  rests  by 
thrust  on  the  slate  formation  there  appear  at  least  two  possible 
ways  to  account  for  the  relations  on  Grand  Isle  and  of  Grand 
Isle  to  the  mainland  by  thrusting: 

1.  Prior  to  the  major  thrust,  as  it  may  perhaps  be  called, 
that  carried  the  quartzite  over  on  the  "Utica,"  as  now  shown 
along  the  mainland,  there  was  reverse  faulting  and  minor  thrust- 
ing by  which  the  limestones  lying  east  of  what  is  now  Grand  Isle 
were  broken,  perhaps  because  of  the  massive  character  of  the 
Beekmantown-Chazy  strata,  and  thrust  up  and  over  the  "Utica." 
In  this  deformation  the  slates  were  tilted  and  overturned.  As 
the  heavy  limestone  strata  rode  over  them  they  were  further 
jammed  beneath  the  load  and  by  the  drag  and  often  broken  and 
mashed.  The  limestones  themselves  were  broken  and  moved 
more  or  less  against  each  other.  At  this  time  were  formed  the 
deformational    features   which   they   show.     Subsequently   there 


254  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

occurred  some  normal  faulting,  perhaps  differential  in  the  same 
episode,  and  as  a  deformation  perhaps  repeated.  Before  the 
normal  fault  displacements  presumably  thrusting  had  ceased. 
Before  it  had  ceased  perhaps  the  stresses  which  had  been  only 
partially  eased  by  the  reverse  faulting  and  minor  thrusting  just 
referred  to  produced  a  great  thrust  that  carried  the  basal  Cam- 
brian up  through  the  "Utica"  and  drove  the  former  westward 
over  the  younger  rocks,  and  over  those  which  now  form  Grand 
Isle.  But  it  has  already  been  remarked  that  if  the  quartzite  once 
extended  very  much  farther  west  of  its  present  edge  along  the 
shore  of  the  mainland  it  seems  somewhat  remarkable  that  some 
remnant  of  its  westward  extension  has  not  been  preserved,  unless 
the  mainland  is  a  downfaulted  block  with  reference  to  the  lake 
region  which  does  not  seem  probable.  According  to  this  postu- 
late, however,  it  is  not  necessary  to  assume  that  the  quartzite  once 
covered  what  is  now  Grand  Isle. 

2.  The  limestone  strata  of  Grand  Isle  once  belonged  to  a 
region  that  lay  eastward  from  Grand  Isle  and  the  "Utica"  slate 
formation  on  it,  one  may  not  say  how  far.  They  may  have  had 
a  relation  to  the  quartzite-phyllite  formation  entirely  similar  to 
that  now  shown  by  the  limestones  which  have  been  described  as 
lying  on  the  phyllite  formation  at  the  south  in  Benson,  Orwell, 
Sudbury  and  other  parts  of  Addison  County.  At  the  time  this 
region  was  undergoing  the  compression  that  produced  the  various 
thrusts  which  may  now  be  seen,  there  was  at  first  ease  of  stress 
by  shearing  and  minor  faulting  and  thrusting.  Then  came  a 
great  thrust,  widely  extended,  cieep  and  powerful,  and  strongly 
resisted  by  the  combined  masses  of  the  quartzite-phyllite  forma- 
tion and  the  heavy  strata  of  limestone  which  lay  on  the  former. 
The  great  thrust  cut  through  the  various  rocks  along  an  irregular 
plane  that  often  intersected  the  quartzite,  but  often  also  passed 
from  that  formation  into  the  overlying  limestone  strata  and  cut 
irregularly  through  them.  As  this  rupture  developed,  the  mass 
above  rode  over  the  mass  below.  Sometimes  the  quartzite  and 
sometimes  the  limestone  was  brought  to  rest  upon  the  slate. 
When  the  thrust  left  the  quartzite-phyllite  formation  and  cut 
into  the  limestone  the  former  was  left  at  depth  west  of  the  pre- 
sumable line  of  emergence  of  the  thrust  at  its  surface.  Not  only 
would  such  a  thrust  plane  as  has  been  postulated  be  very  irre- 
gular as  a  plane,  but  the  line  at  which  it  cut  the  surface  originally 
and  its  trace  after  erosion  would  probably  be  very  irregular  and 
sinuous.  It  is  even  conceivable  that  such  a  plane  would  have  cut 
through  a  great  thickness  of  Beekmantown,  Chazy  and  Trenton 
beds  in  such  a  way  as  to  carry  Beekmantown  here.  Chazy  there 
and  Trenton  at  still  other  places  on  the  "Utica."  After,  and 
perhaps  a  long  time  after,  such  thrusting  as  has  just  been  sup- 
posed had  ceased,  there  would  have  occurred  normal  faulting. 
The  laterally  disturbed  masses  were  now  chopped  more  or  less 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  255 

vertically  and  displaced.  Some  of  the  relations  on  the  island 
now  existing  or  apparent,  might  thus  be  explained.  By  such  an 
hypothesis  of  thrusting  as  just  developed,  the  quartzite  probably 
never  lay  over  what  is  now  Grand  Isle,  although  it  may  once 
have  overlain  a  part  of  what  is  now  lake  between  the  islands 


Figure  21.  A  generalized  section  to  show  the  writer's  interpretation  of  the 
present  relations  of  formations  along  the  eastern  shore  of  Lake  Cham- 
plain  north  of  Burlington.  The  relations  shown  on  the  mainland  are 
drawn  from  studies  near  St.  Albans  Bay.  A,  gray  dolomite ;  B,  gray, 
"marbly"  limestone  ;  C,  light-colored,  slaty  phyllite  (Lower  Cambrian)  ; 
D,  limestone  capping  an  island  and  resting  by  thrust  on  folded  "Utica" 
slate,  E.     1-2  thrust  plane. 

and  the  mainland.  At  St.  Albans  Bay  apparently  we  have  the 
thrust  plane  cutting  through  the  limestone  except  at  certain 
places  where  a  bit  of  the  phyllite  was  caught  beneath  it ;  but 
farther  south  at  Malletts  Bay  and  Burlington,  the  plane  passed 
well  down  in  quartzite  and  opposite  here  the  quartzite  conceiv- 
ably once  extended  farther  westward.  The  region  now  repre- 
sented by  the  lake  has  been  excavated  in  "Utica"  shale  and  slate 
after  the  removal  of  overthrust  rock  that  was  partly  quartzite 
and  partly  limestone.  The  writer  has  not  had  opportunity  to 
inspect  the  mainland  on  the  New  York  side  in  a  critical  way ;  but 
certain  relations  seen  farther  south,  near  Benson  Landing,  sug- 
gest that  part  of  an  overthrust  mass  of  Ordovician  limestone 
now  rests  against  the  Adirondack  mass  north  of  Putnam  Station, 
and  one  wonders  how  far  overthrust  may  have  affected  the  New 
York  side.  According  to  this  view  of  the  relations  at  Grand  Isle 
the  limestones  there  could  hardly  have  been  exposed  to  view  by 
erosion  of  overlying  slate;  but  presumably  limestones  similar 
to  those  at  the  surface  exist  at  depth  below  Grand  Isle. 

That  the  various  considerations  just  offered  are  more  than 
speculations  is  proved  by  overthrust  farther  south.  Practically 
on  the  meridian  of  Grand  Isle  and  60  miles  south  of  it  along  the 
east  shore  of  Lake  Champlain  in  Orwell,  as  has  been  described,  we 
find  the  "Utica"  formation  and  in  some  cases,  apparently,  Black 
River  and  Trenton,  rocks,  overridden  by  members  of  the  Beek- 
mantown  formation  and  perhaps  older  beds  which  also  have  been 
cut  through  in  such  a  way  as  now  to  carry  one  horizon  and  now 
another  over  on  the  slates.  The  erosion  of  the  overthrust  lime- 
stones at  places  in  western  Orwell  has  exposed  the  "Utica"  slates 
which  are  sometimes  inundated  and  sometimes  not.  Here  again 
the  quartzite-phyllite  formation  lies  to  the  east  and  over  it  the 


256  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

limestones  of  western  Orwell  seem  to  pass  eastward,  as  has  been 
described.  Similar  relations  are  shown  in  Shoreham,  but  in  this 
township,  and  in  Whiting  on  the  east,  the  limestones  have  been 
better  preserved.  The  quartzite-phyllite  formation  emerges  at 
the  present  surface  only  as  a  low  ridge  through  Whiting.  At  the 
west  the  "Potsdam"  of  Shoreham  village  fronts  a  wide  lowland 
partly  swamp  and  partly  hills  of  slate.  Here  we  have  in  process 
of  formation  the  kind  of  hard  rock  surface  and  topography  which 
the  unglaciated  bottom  of  the  lake  would  present,  and  it  becomes 
apparent  that  the  lowest  portion  of  the  Champlain  lowland  is  the 
surface  of  the  rock  bottom  of  the  greatest  depth  of  the  lake. 

*  The  various  detached  masses  of  limestone  found  now  at 
various  places  in  the  region  of  the  lake  seem  to  be  not  simple 
erosion  inliers  of  rock  substantially  resting  where  it  was  formed, 
but  rather  thrust-erosion  inliers  of  rocks  now  more  or  less  re- 
moved from  the  places  of  their  deposition.  Whether  it  is  likely 
that  these  displaced  rocks  have  been  moved  more  than  once  for 
any  distance  from  their  original  sites  may  be  discussed  in  the 
final  summary. 

Mention  has  been  made  of  probable  normal  faults  cutting 
across  the  strike  of  the  rocks  of  Grand  Isle.  These  undoubtedly 
pass  down  into  the  slate  formation.  Numerous  dikes  of  igneous 
rocks  cut  through  the  slates  and  limestones  along  the  shore  and 
inland.  These  dikes  usually  show  no  evidence  of  great  disturb- 
ance after  their  formation.  They  were  formed  after  the  lime- 
stones came  to  have  their  present  relations  to  the  slates  and 
probably  after  or  during  the  subsequent  period  of  normal  fault- 
ing. In  the  clifif  south  of  the  Grand  Isle  end  of  Sand  Bar  Bridge 
there  is  a  dike  that  gives  some  suggestion  that  it  has  been  dis- 
turbed, but  not  greatly.  Perhaps  it  would  be  possible  to  explain 
its  features  as  due  to  the  character  of  the  original  fissure;  in  the 
limestones,  while  there  is  some  offsetting  here  and  there,  it  is 
evidently  due  to  the  dike  rocks  following  a  previous  small  lateral 
displacement.  Igneous  intrusion  in  the  form  of  dikes  is  wide- 
spread on  the  island,  and  on  the  mainland  even  southward  to  and 
in  the  Taconic  region. 

GENERAL  SUMMARY. 

The  studies  offered  in  the  preceding  pages  were  begun  with 
the  definite  idea  of  trying  to  get  some  light  on  the  plan  of  struc- 
ture of  the  rocks  of  western  Vermont.  As  details  accumulated 
it  became  apparent  that  many  different  areas  presented  similar 
phenomena  involving  similar  rocks  and  the  search  began  for 
some  principle  that  would  unify  the  various  features  of  the  field 
relations  and  explain  the  apparent  anomalies. 

Suggestions  have  been  offered  in  the  preceding  discussion 
at  several  places  as  to  interpretations  that  might  be  put  upon 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  257 

field  relations ;  but  it  has  been  the  writer's  experience  that  hardly 
a  single  area  sufficed  to  explain  completely  its  own  structural 
features.  At  several  places  also  certain  questions  which  the 
field  relations  raised  have  been  formulated  and  the  statement 
made  that  answers  to  them  might  later  be  attempted. 

The  preceding  descriptions  have  shown  the  confusion  that 
prevails  in  the  field,  but  at  the  same  time  have  tried  to  make  it 
plain  that  when  the  surfaces  of  different  areas  are  carefully  com- 
pared there  is  at  many  places  over  a  wide  region  much  apparent 
uniformity  in  the  relation  which  certain  rocks  bear  to  each  other 
when  such  differences  as  metamorphism  and  present  condition  of 
erosion  are  taken  into  account.  Careful  examination  also  brings 
out  the  existence  of  certain  kinds  of  deformation  in  the  rocks  of 
the  region  which  having  once  been  seen  are  readily  recognized 
at  many  places  and  soon  impress  one  as  being  characteristic. 
The  resemblances  that  appear  from  place  to  place  grow  upon 
one  and  the  differences  stand  out  less  prominently  until  the  time 
comes  when  it  seems  possible  to  discern  some  order  in  the  midst 
of  the  confusion. 

The  first  working  hypothesis  which  suggests  itself  is  that  the 
key  to  the  present  relations  is  that  of  secondary  deformation  of 
the  rocks.  They  have  been  profoundly  disturbed.  Underneath 
their  present  static  relations  and  immobility  it  seems  possible  in 
imagination  to  see  them  once  more  in  action.  While  the  changes 
which  have  been  wrought  throughout  the  long  time  that  has 
doubtless  elapsed  since  the  rocks  underwent  their  major  deforma- 
tions have  greatly  dimmed  the  complete  picture,  and  the  light 
from  scattered  localities  gives  only  an  uncertain  illumination  of 
some  features,  encouragement  is  experienced  in  the  fact  that  the 
main  outlines  come  out  with  increasing  sharpness  as  new  areas 
are  examined. 

In  presenting  this  summary  and  in  inventing  hypotheses 
by  which  to  try  and  explain  the  various  structural  features  and 
the  history  of  the  region  as  a  whole,  there  are  several  apparently 
important  field  relations  that  should  be  kept  in  mind  more  par- 
ticularly to  bring  out  unity  of  structure.  With  these  it  would 
seem  the  minor  differences  must  be  reconciled. 

1.  The  great  north  and  south  extent  along  the  western  edge 
of  the  Green  Mountain  plateau  and  eastern  portion  of  the  Ver- 
mont valley  in  Vermont,  from  Pownal  to  Middlebury  and  beyond, 
of  a  similar  series  of  rocks  comprising  conformable,  thick-bedded 
and  thin-bedded  quartzites  and  interbedded  schists  at  the  base, 
followed  by  dolomites  and  interbedded  dolomites  and  quartzites. 

2.  The  conformability,  as  shown  at  Bennington,  of  the  dif- 
ferent rocks  named  in  1  in  the  order  of  (a)  quartzite-schist 
formation;  (b)  dolomite  or  dolomitic  limestone;  (c)  interbedded 
dolomites  and  quartzites. 


258  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

3.  The  occurrence  of  this  series  at  the  present  time  chiefly 
in  the  areas  mentioned  in  (1)  and  the  predominance  of  the  upper 
members  in  the  valley  and  lowland,  where  they  appear  sometimes 
in  conformable  relation  with  the  quartzite  member  of  the  series 
and  where  sometimes  the  interbedded  rocks  rest  directly  on 
marble,  or  directly  on  quartzite,  and  apparently  at  some  places 
on  an  interbedded  quartzite-schist  formation.  The  frequent  oc- 
currence of  a  dolomite  resting  on  the  marble  or  involved  with 
it,  which  dolomite  differs  from  other  dolomite  with  which  it  is  in 
frequent  proximate  field  association  and  seems  to  belong  to  the 
same  general  formation  to  which  the  quartzite  and  interbedded 
dolomites  and  quartzites  belong. 

4.  The  present  absence  of  this  series  just  described,  in  its 
completeness,  west  of  the  Vermont  valley. 

5.  The  wide  distribution  west  of  the  Vermont  valley,  in- 
cluding parts  at  least  of  the  main  Taconic  range,  of  a  terrigenous 
formation  made  up  of  black  phyllites  or  schists,  lighter-colored, 
fissile  or  slaty  phyllites,  and  more  or  less  massive  quartzite  which 
are  rather  plainly  interstratified,  as  shown  in  surface  sections 
at  numerous  places  from  the  latitude  of  Pownal  to  that  of  Sud- 
bury and  which  can  be  discerned  in  fault  scarps  at  places  west  of 
the  range  in  the  Taconic  hills. 

6.  The  striking  similarity  among  black  phyllites  and  other 
members  of  this  terrigenous  formation  at  most  places  over  the 
region  of  its  present  distribution,  with  certain  variations  appear- 
ing on  account  of  greater  metamorphism  in  some  areas.  The 
close  geographical  and  geological  association  which  this  forma- 
tion has  with  the  quartzite-dolomite  series  described  above  and 
the  similar  north  and  south  extension  of  the  two  in  this  associa- 
tion at  the  east  along  the  region  of  the  Vermont  valley. 

7.  The  practical  restriction  of  the  outcrops  of  the  marble 
formation  to  the  region  of  the  Vermont  valley,  or  to  the  incisions 
along  the  eastern  border  of  the  Taconic  range,  or  to  the  eastern 
part  of  the  Champlain  lowland ;  and  the  exposure  by  erosion  of 
patches,  belts,  or  other  outcrops  of  the  marble  from  beneath  the 
calcareous  members  of  the  quartzite-dolomite  series  described 
above  (3),  and  apparently  also  from  beneath  masses  of  terrige- 
nous rocks  having  the  interbedded  structure  and  composition 
mentioned  above  (5). 

8.  The   probable   Lower   Cambrian   age   of   the   quartzite- 
dolomite  series  on  the  bases  of  fossils  found  in  the  quartzite  and ' 
at  some  places  in  the  calcareous  members,  in  connection  with  the 
conformability  shown  by  the  members  of  the  series. 

9.  The  clearly  disturbed  condition  through  compression  of 
the  Lower  Cambrian  series  along  the  western  margin  of  the 
plateau,  involving  displacements  of  one  part  in  relation  to  another 
part  of  the  series  and  the  displacement  of  the  whole  series  or 
parts  of  it  by  overlap  on  other  rocks ;  the  former  to  be  observed 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  259 

all  along  the  western  edge  of  the  plateau  and  the  latter  to  be 
noted  at  many  places,  at  some  more  clearly  than  at  others. 

10.  The  practical  impossibility  of  separating  on  any  basis, 
except  somewhat  different  mineralogical  composition  clearly  due 
to  metamorphic  changes,  rocks  found  on  the  edge  of  the  plateau 
and  others  found  in  the  Taconic  range  and  its  physiographic  out- 
liers and  also  in  the  hills  of  southwestern  Brandon,  and  of  Sud- 
bury, Orwell,  Benson,  Hubbardton,  Pownal,  Bennington,  Shafts- 
bury,  Pawlet,  Rupert,  and  other  townships,  some  of  which  have 
been  mapped  as  "Berkshire  Schist"  and  some  as  "Cambrian." 
The  wide  distribution  at  the  present  erosion  surface  of  all  the 
characteristic  members  of  this  terrigenous  formation  from  Pownal 
to  Sudbury  and  possibly  also  to  the  northern  part  of  the  State, 
although  the  writer's  examination  of  the  region  along  the  lake 
north  of  Burlington  gave  only  the  quartzite  and  the  lighter- 
colored  phyllites,  and  between  Whiting  and  Burlington  only  the 
quartzite  ("Red  Sandrock"). 

11.  The  apparent  wide  distribution,  with  interruptions  over 
large  areas  clearly  due  in  part  to  erosion  and  probably  in  part 
to  previous  disturbances  which  affected  the  ways  in  which  erosion 
could  work,  of  Ordovician  limestones  and  their  metamorphosed 
derivatives  on  the  terrigenous  formation  which  has  been  described, 
found  in  Whiting,  Sudbury,  Brandon,  Orwell,  Benson,  West 
Haven,  Hubbardton,  Danby,  Tinmouth,  Rupert,  Shaftsbury,  and 
also  at  the  north  near  St.  Albans.  The  occurrence  of  similar 
limestones  on  the  quartzite,  or  "Red  Sandrock,"  of  Snake  and 
Buck  mountains,  and  in  their  vicinity.  The  greater  continuity  at 
the  present  surface  of  the  Ordovician  calcareous  rocks  in  Shore- 
ham,  Whiting,  northern  Sudbury  and  Orwell,  and  the  much 
more  fragmentary  condition  of  the  same  rocks  at  the  south  in 
the  Taconic  hills. 

13.  The  impossibility  of  assigning  age  to  the  terrigenous 
rock  on  the  basis  of  the  limestone  associated  with  it  in  all  the 
places  examined. 

14.  The  overlap  in  some  places  of  quartzite  of  Lower  Cam- 
brian age  (at  and  north  of  Burlington)  and  at  other  places  of 
Ordovician  limestones,  like  those  which  rest  on  the  terrigenous 
rocks,  including  the  quartzite,  on  the  slates  and  shales  of  the 
so-called  "Utica"  formation,  to  be  seen  at  various  places  along  or 
near  the  eastern  shore  of  Lake  Champlain. 

15.  Evidence  of  repeated  normal  and  reverse  faulting  in  the 
quartzite-dolomite  series,  the  latter  sometimes  causing  the  quartz- 
ite, sometimes  phyllite  to  rest  against  the  dolomite  or  against  the 
interbedded  members,  various  aspects  of  which  faulting  may  be 
seen  at  different  places  from  Bennington  to  Salisbury,  along  the 
eastern  portion  of  the  Vermont  valley. 

16.  Evidence  of  repeated  reverse  faulting  and  of  normal 
faulting  in  the  overlapping  Ordovician  strata  near  the  lake,  to 
be  seen  in  Shoreham  and  Orwell  townships  and  at  other  places. 


260  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

17.  Evidence  of  disturbance  by  normal  faulting,  and  prob- 
ably also  by  reverse  faulting,  of  the  quartzite-phyllite  formation 
among  the  Taconic  hills. 

18.  Evidence  of  internal  deformation  by  strong  shearing 
of  the  calcareous  rocks  lying  on  the  the  terrigenous  rocks  which 
increases  somewhat  gradually  as  one  goes  eastward  from  the  lake 
region. 

19.  The  highly-metamorphosed  character  of  the  marble  at 
the  east. 

20.  The  more  schistose  condition  of  the  rocks  of  the  main 
Taconic  range. 

21.  The  relatively  unaltered  character  in  most  cases  of  the 
rocks  near  the  lake. 

22.  Absence  of  recognizable  Beekmantown  east  of  the  im- 
mediate vicinity  of  the  lake. 

One  of  the  first  difficulties  that  was  encountered  in  applying 
any  hypothesis  to  explain  present  structure  as  a  result  of  defor- 
mation was  that  of  arriving  at  a  feeling  of  certainty  as  to  the 
age  of  the  terrigenous  formation  with  which  the  fossiliferous 
Chazy-Trenton  limestones  are  so  frequently  associated  and  in' 
such  apparent  relations  as  to  leave  no  doubt  of  the  superjacent 
position  of  the  limestones  with  respect  to  the  terrigenous  rocks. 
Some  of  these  terrigenous  rocks  have  been  called  Ordovician  and 
and  others  Cambrian  in  areas  in  which  the  writer  was  unable  to 
see  a  valid  distinction.  The  writer  has  satisfied  himself  on  the 
point  that  the  age  of  the  terrigenous  rock  cannot  always  be  told 
from  the  limestone  associated  with  it — it  may  be  in  some  cases 
apparently  (Cambrian)  ;  but  if  this  is  the  fact  it  leaves  the  age 
of  quartzite-phyllite  formation  as  a  whole  still  a  question.  Espe- 
cially should  it  be  noted  that  the  presence  of  Ordovician  hme- 
stone  with  phyllite  is  not  indicative  of  a  similar  age  for  the  latter 
in  any  cases  which  the  writer  has  examined.  The  limestone  has 
the  character  of  an  overlapping  formation  on  the  terrigenous 
mass.  The  next  difficulty  in  applying  an  hypothesis  is  to  get  the 
limestone  on  the  terrigenous  formation.  How  did  it  come  there  ? 
In  trying  to  answer  this  question  another  difficulty  appears.  The 
writer  was  unable  to  find  any  visible  contacts  of  limestone  on 
the  quartzite  or  phyllite.  In  southern  Shaftsbury  the  two  are 
very  near  at  the  present  surface  and  the  limestone  here  is  greatly 
mashed  and  broken,  affording  a  suggestion  that  it  was  thrust  on 
the  phyllite ;  but  the  field  relation  is  not  conclusive.  In  other 
words,  there  is  nothing  to  show  that  the  limestone  might  not  have 
been  deposited  on  the  phyllite,  or  at  least  on  contiguous  phyllite, 
and  have  been  slightly  disturbed  later,  or  that  it  must  have  come 
to  its  present  position  from  some  more  or  less  remote  place.  In 
other  places  the  two  rocks  are  near  together,  but  the  question  of 
whether  the  apparent  overlap  is  one  of  deposition  or  one  of  thrust 
apparently  may  not  be  positively  settled  by  the  contact  relations. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  261 

although  it  has  not  proved  possible  to  find  any  rock  that  might 
be  thought  of  as  representing  the  shore  accumulation  along  the 
transgressing  strand  line  of  a  sea  advancing  upon  terrigenous 
rock.  If  the  ovferlap  i.s  one  of  depositon  it  would  seem  that  the 
limestone  was  probably  laid  down  upon  the  terrigenous  formation 
without  definite  and  continuous  basal  overlapping  member. 

It  would  probably  be  argued  that  the  fact  of  a  subjacent 
position  for  the  terrigenous  formation  with  respect  to  Ordovician 
litnestones  is  not  conclusive  evidence  of  its  greater  age,  in  a 
region  in  which  thrust  deformation  is  regarded  as  the  key  to  the 
structure.  This  probably  must  be  admitted.  What  is  the  prob- 
ability as  one  views  the  region  as  a  whole? 

The  Brandon-Sudbury-Orwell  region  is  one  of  great  interest 
in  connection  with  the  question  of  the  relation  of  quartzite-phyl- 
lite  formation  to  the  Ordovician  limestones.  As  has  been  de- 
scribed, the  terrigenous  rocks  pass  beneath  the  limestones  north- 
ward in  Orwell,  and  also  in  Sudbury,  except  for  a  narrow  ridge 
that  passes  northward  through  Whiting  to  Weybridge.  Little 
doubt  remains  that  the  extensive  areas  of  limestone  north  of 
Orwell  and  Sudbury  rest  on  the  northward  continuation  beneath 
them  of  the  terrigenous  rocks  of  the  hills  at  the  south.  The  latter 
rocks  also,  except  for  normal  faulting,  pass  beneath  the  marbles 
and  their  associated  rocks  in  Brandon  and  appear  again  east  of 
Brandon  village.  At  this  place  the  intimate  association  which 
they  have  with  Lower  Cambrian  rocks  makes  the  presumption 
of  a  similar  age  very  strong. 

The  quartzite  of  Snake  and  Buck  mountains  apparently  has 
the  same  relation  to  the  Ordovician  limestones  that  the  phyllites 
of  Whiting  have  and  the  quartzite  joins  northeastward  with  lin- 
important  interruptions  at  the  surface  through  Monkton  with  the 
rocks  of  the  plateau,  and  southward  after  a  more  extensive  sur- 
face interruption  under  the  limestones  with  the  quartzite-phyllite 
hills  of  Orwell.  Through  the  quartzite  of  Charlotte  and  Shel- 
burne  and  northward,  the  southern  quartzite  joins  with  that  north 
of  Burlington  which  carries  Lower  Cambrian  fossils.  Southward 
the  hills  of  Orwell  join  with  similar  rocks  that  carry  Lower 
Cambrian  fossils.  It  would  certainly  seem  that  from  surface  con- 
tinuity, or  what  amounts  practically  to  it,  since  the  fact  of  similar 
limestone  resting  on  the  different  terrigenous  rocks  is  apparent, 
the  probability  of  the  Lower  Cambrian  age  of  the  quartzite- 
phyllite  formation  underlying  the  limestones  of  Benson,  Orwell, 
Sudbury,  Brandon,  Whiting,  and  probably  even  Bennington  and 
Shaftsbury,  is  strongly  indicated,  as  well  as  the  equivalence  of 
the  quartzite  ("Red  Sandrock")  farther  north  to  the  rocks  of 
the  Taconic  hills.  The  case  would  be  stronger  if  depositional  over- 
lap of  the  limestones  could  be  proved  or  shown  to  be  very  prob- 
able. It  is  hard  to  prove  the  point.  In  Orwell  and  Benson  the 
limestones  have  unquestionably  been  greatly  disturbed  and  per- 


262  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

haps  moved  some  distance  from  the  east,  if  the  contrast  which 
they  exhibit  with  the  rocks  of  the  lake  region  that  have  been  over- 
ridden means  anything  in  this  connection ;  but  they  do  not  give 
an  impression  that  is  at  all  conclusive  of  having  been  transported 
from  a  distance  and  superposed  on  the  terrigenous  rocks  on  which 
they  lie.  If  the  point  of  the  former  widespread  covering  of  the 
terrigenous  rocks  by  the  limestones  be  accepted  as  probable,  then 
there  is  involved  a  long  distance  from  east  to  west  for  these 
limestones  to  have  been  moved  bodily  across  it  over  the  rocks  on 
which  they  now  lie,  although  it  is  quite  conceivable  that  they  could 
have  been  disturbed  from  their  original  positions  and  probably 
were.  It  would  appear  more  probable  from  the  appearance 
which  they  now  present  that  if  they  had  a  movement  of  transla- 
tion from  the  east  it  was  one  in  which  the  mass  beneath  par- 
ticipated ;  that,  in  other  words,  they  really  "rode"  along  the  thrust 
plane  on  a  mass  of  terrigenous  rock  that  transported  them.  From 
all  the  viewpoints  that  the  writer  could  utilize  after  a  careful  field 
study,  it  appears  to  him  quite  as  if  not  more  probable  that 
the  limestones  were  deposited  on  the  terrigenous  rocks.  All  the 
field  relations  suggest  such  a  history  rather  than  that  they  have 
come  to  be  distributed  on  the  quartzite-phyllite  formation  by 
thrust.  On  this  view  then  the  latter  formation  is  older  than  the 
limestones  and  if  it  may  be  made  to  appear  extremely  probable 
that  there  is  unity  in  the  terrigenous  formation  over  all  the  areas 
where  it  shows  essentially  the  same  characters,  except  perhaps 
for  difference  in  metamorphism,  then  the  principle  of  thrust  as 
the  key  to  structure  in  the  presence  of  what  may  be  actually  seen 
of  overlap  in  the  region  seems  to  apply.  Some  applications  of  it 
have  already  been  made  without,  however,  stating  much  about 
the  probable  relative  age  of  the  terrigenous  rocks,  except  that 
they  had  suggestive  association  with  the  Lower  Cambrian  rocks 
at  the  east  and  that  they  seemed  unquestionably  to  be  normally 
beneath  the  limestones,  including  the  marble. 

In  connection  with  the  discussion  or  argument  just  given  it 
should  be  remembered  that  on  previous  pages  it  has  been  con- 
tended that  there  is  nothing  which  the  writer  has  been  able  to 
see  in  the  terrigenous  rocks  of  the  Orwell-Sudbury  hills  that 
supports  the  idea  that  two  terranes  are  there  represented.  The 
rocks  seem  to  compose  a  formational  unit.  The  question  is,  What 
is  the  age  of  the  unit?  Whether  one  regards  it  as  Cambrian  or 
as  Ordovician,  the  problem  remains  of  accounting  for  the  superior 
position  of  the  limestones.  Accordingly,  the  field  relations  were 
considered  from  the  point  of  view  of  any  of  the  terrigenous  rocks 
being  of  Ordovician  age  to  see  if  the  principle  of  thrust  which 
has  to  be  recognized  could  be  applied  on  that  basis. 

At  this  point  it  seems  advisable  to  call  attention  again  to  one 
other  relation  which,  in  the  writer's  opinion,  argues  against  the 
terrigenous  rocks  under  discussion  being  younger  than  the  lime- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  263 

stones,  including  the  marbles.  Over  the  extensive  limestone  areas 
north  of  Brandon,  Sudbury  and  Orwell  we  do  not  find  any  schist 
above  the  limestone.  The  strongest  argument  for  the  younger 
age  of  the  schist  appears  to  be  its  superior  position  at  places 
farther  south.     This  relation  has  already  been  discussed. 

The  idea  that  any  of  the  terrigenous  rocks  under  discussion 
are  of  Ordovician  age  assumes  that  the  limestones  are  in  general 
older  than  such  terrigenous  rocks  and  that  the  latter  represent 
changed  conditions  of  deposition  in  a  sea  which  first  laid  down  the 
limestones  on  an  older  base,  conformably  or  unconformably.  How 
could  the  conditions  have  permitted  change  from  limestone  to 
sand  and  mud  rocks  so  that  now  in  what  is  the  Taconic  range  the 
limestones  could  have  a  covering  of  younger  schist  and  so  that 
conditions  elsewhere  in  the  vicinity,  such  as  north  of  the  range, 
could  be  as  they  now  are?  It  is  still  conceivable,  if  Ordovician 
limestones  were  succeeded  and  covered  by  terrigenous  deposits, 
that  during  a  period  of  compression  and  thrust,  Cambrian  rocks 
could  have  been  brought  to  lie  on  the  Ordovician  schists,  while 
the  Cambrian  rocks  passed  under  the  limestone  at  depth. 

If  the  schist  capping  Mt.  Anthony  in  Bennington  and  Dorset 
Mountain  and  the  ridge  in  between  be  regarded  as  of  Ordovician 
age,  passing  by  resemblances  which  much  of  this  schist  shows, 
except  for  metamorphism  to  rocks  that  have  been  shown  as 
Cambrian  on  maps  which  represent  the  schist  as  Ordovician, 
many  of  the  field  relations  are  apparently  not  impossible  of  ex- 
planation while  allowing  the  presence  of  deformation  of  the  re- 
gion by  thrusts. 

One  may  first  imagine  an  eastward  transgression  of  an  Or- 
dovician sea  probably  over  an  eroded  Cambrian  floor  with  depo- 
sition of  limestone.  If  after  the  deposition  of  a  certain  amount 
of  limestone  an  elevation  should  have  occurred  landward,  it  is 
possible  to  imagine  that  terrigenous  deposits  would  have  been 
carried  westward  out  over  the  limestone  which  had  been  over- 
lapping the  older  land.  Deposition  of  limestone  would  have  been 
halted  landward  but  might  have  continued  at  the  west  and  at  other 
places,  so  to  speak,  while  the  muds  and  sands  under  the  new  con- 
ditions were  making  at  places  at  the  east.  It  is  of  course  pos- 
sible to  imagine  that  these  terrigenous  rocks  were  restricted  in 
their  distribution  and  were  not  laid  down  everywhere  along  the 
changing  strand.  While  some  effort  is  required  to  imagine  dif- 
ferent conditions  of  deposition  in  such  close  proximity  as  to  give 
originally  the  same  abrupt  passage  from  schist  to  limestone  that 
is  now  to  be  seen  at  the  northern  end  of  the  Taconic  range,  it  is 
not  inconceivable.  In  some  way,  according  to  the  terms  so  far 
given  of  this  hypothesis,  the  absence  of  the  schists  over  the  mar- 
bles and  limestones  at  the  north  must  be  explained,  it  being 
assumed  that  the  limestones  at  the  north  and  those  underlying  the 
schist  at  the  south  are  essentially  the  same  and  that  both  rest  on 


284  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

a  similar  base.  We  may  further  imagine  that  the  westward 
distribution  by  seaward  overlap  of  muds  and  sands  was  re- 
stricted, perhaps  in  some  places  more  than  others,  in  its  extent 
and  that  at  the  west  these  deposits  graded  laterally  into  more 
limy  muds  which  graded  downward  into  Trenton  and  upward 
into  the  so-called  "Utica."  We  may  imagine  that  at  certain 
places  the  deposition  of  limestone  continued  practically  during 
the  whole  time  that  the  schists  were  making  at  other  places,  or 
that  at  places  the  limestones  were  succeeded  by  other  deposits 
which  were  of  such  character  that  they  could  be  easily  eroded  and 
therefore  do  not  now  appear  above  the  limestone,  as  north  of  the 
Taconic  range  for  instance. 

The  hypothesis  just  considered  is  in  reality  the  theoretical 
extension  of  another  involving  other  field  relations  and  considera- 
tions, more  especially  the  occurrence  of  essentially  equivalent 
limestone  strata  lying  on  a  terrigenous  mass,  composed  every- 
where of  parts  indistinguishable  in  one  place  from  those  of  an- 
other, and  which  seems  to  be  a  formational  unit,  and  which 
occurrence,  as  discussed  above,  seems  to  be  due  to  the  deposition 
during  the  Ordovician  period,  and  perhaps  the  latter  part  of  the 
Cambrian  period,  of  the  limestones  of  those  periods  on  the  mass 
of  terrigenous  material  which  now  underlies  the  limestones.  The 
field  relations  indicate  unconformity  of  contact  although  actual 
contact  was  not  found. 

If  now  we  take  such  evidence  as  we  have  of  the  age  of  the 
terrigenous  substratum,  some  of  which  was  given  above,  and  re- 
gard it  as  of  probable  Cambrian  age  and  probably  largely  Lower 
Cambrian,  from  what  we  know  of  the  geology  of  surrounding 
regions  as  well  as  that  of  western  Vermont  itself,  we  may  formu- 
late more  definitely  another  hypothesis  to  explain  certain  primary 
relations  which  preceded  the  disturbance  of  the  region  by  great 
thrusts. 

We  may  imagine  the  Paleozoic  history  of  the  region  to  have 
begun  with  the  deposition  of  extensive  masses  of  terrigenous 
materials  marked  by  a  thick  sandstone  at  the  base  overlapping 
from  the  west  on  an  older  land  north  and  south  all  along  through 
what  is  now  western  Vermont  and  certainly  also  beyond  its  con- 
fines. As  the  sea  deepened  offshore,  muds  mingled  with  the 
sands  until  a  great  thickness  was  accumulated.  Oscillations  of 
level  or  other  conditions,  perhaps  a  combination,  finally  produced 
a  mass  of  interstratified  mud  and  sand.  We  may  further  imagine 
that  there  was  lateral  variation  in  these  terrigenous  deposits. 
Possibly  where  rivers  flowed  into  the  sea  the  sands  were  carried 
farther  offshore  and  formed  deltas  between  deposits  of  finer 
materials  extending  in  either  direction,  north  and  south.  On 
these  deltas  the  ebb  tides  and  periodic  diminution  of  river  floods 
exposed  the  sands  to  the  weather  and  the  oxidizing  agencies  pro- 
duced the  red  color  now  marked  by  certain  members  of  these 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  265 

rocks  on  which  the  Hmestones  now  seem  to  lie.  Finally,  condi- 
tions would  have  permitted  the  deposition  of  the  dolomitic  lime- 
stones and  interbedded  dolomites  and  quartzites  so  widely  present 
north  and  south  in  association  with  the  quartzite-schist  series. 
The  hypothesis  as  thus  far  developed  does  not  assume  that  the 
present  geographical  relations  between  the  rocks  of  the  Taconic 
region  that  are  being  regarded  as  Lower  Cambrian  and  the  Lower 
Cambrian  rocks  along  the  western  edge  of  the  plateau  and  in  the 
Vermont  valley  was  the  one  which  obtained  when  these  respective 
rocks  were  forming;  but  on  the  contrary  recognizes  that  they 
are  now  separated  by  thrusts.  Nevertheless,  the  calcareous  rocks 
of  the  Lower  Cambrian  series  were  probably  once  present  over 
the  Lower  Cambrian  terrigenous  rocks  of  the  Taconic  hills. 

After  deposition  of  Cambrian  sediments  had  continued  for 
a  time,  perhaps  for  Middle  and  part  or  all  of  Upper  Cambrian 
time  as  well  as  during  the  Lower  Cambrian  period,  a  disturb- 
ance may  be  thought  of  as  having  folded  or  otherwise  deformed 
the  Cambrian  beds  and  raised  them  above  the  sea.  Erosion 
would  have  followed  and  a  considerable  but  unknown  mass  of 
rocks  presumably  would  have  been  removed,  exposing  the  Lower 
Cambrian  rocks.  The  changes  which  the  Cambrian  rocks  under- 
went during  this  disturbance  could  be  thought  of  as  having  pro- 
duced some  of  the  differences  now  apparent  between  them  and 
the  limestones  which  rest  on  them  at  many  places.  It  is  notice- 
able, from  east  to  west,  that  the  terrigenous  rocks  on  which  the 
limestones  lie  are  more  uniformly  altered  than  are  the  limestones ; 
they  present  less  variation  in  metamorphism  over  the  same  areas. 

Finally  came  a  submergence  of  this  denuded  Cambrian  sur- 
face and  the  deposition  of  a  series  of  calcareous  rocks,  one  can 
hardly  say  at  just  what  time  because  the  bottom  of  series  is  not 
now  present  in  western  Vermont,  as  the  oldest  Ordovician  lime- 
stone or  sandstone  usually  rests  by  thrust  on  much  younger  strata. 
One  cannot  say  what  may  be  present  at  depth  underneath  a  prob- 
ably great  thickness  of  Ordovician  rocks  in  the  lake  region  which 
have  been  overridden  by  great  masses  of  other  rocks,  including 
some  Ordovician.  The  hypothesis  of  Ordovician  deposition  that 
is  being  developed  is  in  fact  erected  on  the  basis  of  the  overriding 
mass,  in  largest  part. 

Near  the  lake  the  great  thrust  plane  along  which  were  car- 
ried the  rocks  from  the  east  over  on  those  at  the  west,  sheared 
away  from  the  terrigenous  rock  into  and  through  various  Ordo- 
vician horizons,  but  apparently  through  nothing  older  than  the 
so-called  "Potsdam"  which  has  been  described. 

The  deposition  of  the  limestones  apparently  proceeded  by 
overlap  eastward,  laying  down  first,  at  the  west,  the  Beekman- 
town  and  by  progressive  advance  farther  east  some  Chazy  and 
Trenton.  What  may  have  come  above  the  limestones  at  the  east 
has  already  been  discussed.  At  the  west  we  have  evidence  that 
the  Trenton  was  followed  by  the  "Utica,"  but  this  rock  apparently 


266  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

does  not  now  appear  east  of  the  erosion  margin  of  the  great  thrust 
except  from  beneath  by  exposure  from  erosion,  as  south  of  Mt. 
Philo  in  Ferrisburg  and  Charlotte. 

Such  an  hypothesis  seems  to  offer  a  ready  and  simple  ex- 
planation of  the  occurrence  of  Chazy-Trenton  beds  apparently 
resting  directly  on  the  terrigenous  formation  in  Orwell,  Sudbury 
and  Benson,  if  the  latter  formation  is  the  Cambrian.  It  also 
permits  the  interpretation  that  the  fragmentary  areas  of  Ordo- 
vician  limestone  in  the  Taconic  hills  are  erosion  outliers  resting 
unconformably  upon  the  rocks  beneath.  The  hypothesis  does 
not  necessarily  call  for  the  interpretation  of  schist  now  resting 
on  the  limestone,  or  marble,  as  younger,  in  view  of  the  possibili- 
ties of  modifications  by  thrust  deformation.  One  thing  that 
seems  to  support  the  idea  of  depositional  overlap  is  the  geograph- 
ical extension  of  tlfe  limestone  over  the  terrigenous  formation, 
if  erosion  is  taken  into  account. 

To  some  it  would  seem  almost  incredible  that  the  Beekman- 
town  which  has  such  a  tremendous  apparent  thickness  near  the 
lake  was  not  deposited  over  what  are  now  the  Taconic  region  and 
the  Vermont  valley.  Seely,  in  fact,  could  not  believe  it.  The 
fact  remains  that  the  Beekmantown  has  not  been  positively  recog- 
nized away  from  the  lake  in  what  is  to  be  regarded  as  the  mass 
that  has  been  in  some  degree  transported  from  the  eastward.  Is 
it  possible  that  it  could  have  been  deposited?  Is  it  possible,  for 
example,  that  the  marble  is  the  Beekmantown?  Allowing  again 
the  necessity  for  recognizing  thrusts,  is  it  possible  to  explain  the 
present  relative  position  of  Chazy-Trenton  limestones  and  the 
terrigenous  rocks  of  the  Taconic  hills  in  Orwell  and  Sudbury  and 
still  have  the  Beekmantown  in  the  marbles  at  the  east  ?  It  would 
seem  that  in  this  connection  it  is  necessary  to  consider  the  prob- 
ability of  down  faulting  of  the  marble  and  that  some  restoration 
of  the  rocks  along  the  eastern  border  of  the  Vermont  valley  would 
have  to  be  made,  as  has  been  done  above,  in  order  to  weigh  the 
question  properly.  When  such  restoration  is  made  the  probable 
Ordovician  calcareous  rocks  of  the  valley  are  apparently  raised 
to  the  level  of  those  which  lie  on  the  rocks  of  the  Taconic  hills 
and  the  presumption  grows  that  the  marbles  are  younger. 

To  some  the  explanation  of  the  occurrence  of  the  hmestones 
on  the  quartzite-phyllite  formation  by  deposition  might  not  ap- 
peal. It  would  then  be  necessary  to  account  for  the  relation  in 
some  other  way,  say  by  thrust.  Could  a  thrust  plane  have  cut 
through  a  mass  of  rocks  that  lay  to  the  eastward  of  the  present 
Taconic  hills  in  such  way  as  to  carry  everything  that  lay  above 
the  calcareous  rocks  that  now  occur  in  the  Taconic  hills  on  the 
toe  of  the  thrust  and  further  in  such  way  as  to  superpose  these 
Chazy-Trenton  limestones  on  Lower  Cambrian,  at  the  same  time 
pushing  what  lay  on  the  Lower  Cambrian  still  farther  west,  the 
mass  pushed  now  having  disappeared  by  erosion?  It  might  be 
possible,  since  there  seems  to  be  no  necessary  rule  to  govern  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  267 

way  in  which  a  thrust  plane  would  cut  having  once  been  initiated. 
Such  explanation  might  leave  Beekmantown  at  depth  somewhere 
at  the  east.  It  magnifies  more  than  ever  the  principle  of  thrust 
and  the  distance  of  movement.  That  we  must  suppose  that  such 
thrust,  if  it  occurred,  carried  Ordovician  limestones  on  Cambrian 
seems  best  shown  north  of  the  Taconic  hills,  where  the  evidence 
is  strongest  for  the  terrigenous  rock  ("Red  Sandrock")  being 
Cambrian.  If  it  carried  the  limestones  on  Cambrian  there  is  it 
probable  that  it  would  have  elevated  them  to  Ordovician  schists 
only  a  few  miles  to  the  south  in  the  Taconic  hills? 

The  idea  of  depositional  overlap  fits  the  conditions  at  Snake 
and  Buck  mountains  if  we  recognize  the  possibility  of  lateral 
variation  of  the  Lower  Cambrian  sands  and  muds. 

The  proximity  of  the  phyllite  in  the  Whiting- Weybridge  belt 
to  the  quartzite  of  Snake  and  Buck  mountains  offers  no  particular 
difficulty.  The  hypotheses  mentioned  have  not  been  knowingly 
stretched  to  meet  the  facts.  They  take  careful  account  of  studied 
field  relations.  Any  discrepancies  may  be  put  down  for  the  most 
part  as  due  to  differences  of  assignment  of  age  to  certain  rocks 
and  to  other  differences  of  interpretation. 

In  the  descriptions  of  the  various  areas  given  in  the  preced- 
ing pages,  application  has  been  made  of  some  of  the  ideas  that 
have  just  been  developed.  In  the  lake  region  there  is  acceptable 
evidence  which  has  long  been  recognized  of  westward  thrust. 
Perhaps  some  of  the  details  offered  in  this  paper  are  new,  and 
perhaps  some  of  the  explanations  are  original.  It  is  plain  that 
we  must  recognize  the  present  juxtaposition  of  masses  that  were 
once  more  or  less  separated.  When  we  find  the  "Utica"  exposed 
from  beneath  the  mass,  which  we  look  upon  as  having  moved 
from  the  east,  at  some  distance  east  of  the  present  lake  shore,  the 
probability  of  extensive  movement  appeals  strongly.  We  are 
bound  to  consider  the  possibility  that  much  of  the  calcareous 
rock  now  exposed  in  the  lake  region  is  transported  rock.  If 
such  could  be  established  with  much  certainty,  our  ideas  of 
sedimentary  provinces  might  require  modification  in  some 
measure.  We  do  not  now  view  the  rock  where  it  was  originally 
deposited. 

In  Benson  and  Orwell  it  may  appear  that  we  should  recognize 
the  probability  that  a  phyllite  of  Cambrian  age  now  rests  on  a 
slate  of  Ordovician  age  by  thrust.  It  may  be  that  we  shall  have 
to  do  the  same  or  something  similar  at  the  east,  but  there  the 
conditions  are  more  obscure. 

The  possibility  of  extensive  thrust  or  of  any  geographically 
extended  thrust  between  the  plateau  and  the  Taconic  range  does 
not  seem  to  have  received  much  attention  or  credence.  The  evi- 
dence for  thrust  overlap  has  been  cited  and  the  question  discussed 
above.  It  remains  to  consider  a  few  localities  more  specifically 
than  has  been  done. 


268  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Apparently,  without  doing  violence  to  the  hypothesis  of  Cam- 
brian or  post-Cambrian  folding  and  erosion  and  subsequent  Or- 
dovician  overlap,  or  even  to  the  idea  that  the  latter  in  some  way 
brought  terrigenous  rocks  to  rest  on  the  limestone  that  rests  on 
supposed  Cambrian,  it  is  possible  to  imagine  that  at  some  time 
after  the  overlap  occurred,  possibly  after  a  period  of  erosion,  but 
not  necessarily,  during  a  period  of  compression  a  part  of  the 
Cambrian  quartzite-schist  formation  was  broken  and  thrust 
through  and  over  the  limestone.  In  this  way  a  schist  could  have 
come  to  overlie  a  limestone  or  a  marble  and  might  appear  in  a 
greatly  disturbed  region  to  be  conformable.  But  the  possibilities 
seemingly  do  not  end  here.  If  the  Ordovician  limestone  were 
succeeded  upward  by  terrigenous  rock,  in  some  such  way  as 
described  above,  or  otherwise,  these  might  even  be  overthrust  by 
older  terrigenous  rocks  so  that  Cambrian  quartzite  or  schist 
might  come  to  lie  on  Ordovician  schist,  while  the  former  underlay 
the  limestone  at  depth. 

It  appears  that  the  metamorphism  shown  by  the  schist  of  the 
Taconic  range,  which  it  should  be  noted  in  many  cases,  does  not 
exceed  that  shown  by  the  rocks  of  some  of  its  foothills,  could 
readily  have  been  produced  in  muds  of  Cambrian  age  and  if  these 
should  have  by  thrust  been  elevated  and  shoved  westward  on 
Ordovician  calcareous  rocks,  they  might  readily  have  come  into 
such  relation  with  less  altered  or  originally  somewhat  different 
terrigenous  rocks  as  to  give  an  appearance  of  being  wholly  dif- 
ferent in  age,  which  aspect  would  be  heightened  by  the  fact  of 
their  position  relative  to  the  limestone.  In  a  region  of  thrust 
lithological  transitions  as  indications  of  increasing  metamorphism 
in  relatively  undisturbed  rocks  and  therefore  as  indications  of 
similar  age,  may  have  unsuspected  significance. 

The  relations  around  Bennington  are  very  complicated  and 
those  are  apparently  most  so  which  at  first  appear  simple.  It 
would  appear  on  the  basis  of  general  unity  of  structure  of  the 
rocks  over  a  wide  region  that  the  conditions  at  Bennington  should 
be  capable  of  any  explanation  which  should  essentially  satisfy 
the  conditions  farther  north  in  the  Vermont  valley.  On  the  basis 
of  downfaulting,  evidence  for  which  is  as  strong  at  Bennington 
as  at  any  place  in  the  valley,  one  may  attempt  a  restoration  like 
that  which  was  imagined  for  the  valley  around  Dorset.  The 
elements  of  uncertainty  are  many.  The  conditions  south  of  the 
latitude  of  North  Bennington  are  somewhat  different  from  those 
north  of  it,  which  lends  some  support  to  the  idea  of  transverse 
or  east-west  faulting  between  Mt.  Anthony  and  West  Mountain. 
The  elevation  of  the  surface  of  the  valley  quartzite  south  of 
Bennington  to  that  of  the  plateau  would  carry  a  certain  amount 
of  the  calcareous  rocks  of  the  Cambrian  upward,  but  it  is  not 
clear  that  it  would  carry  all  as  the  interbedded  rocks  along  the 
western  side  of  the  valley  south  of  Bennington  may  not  rest  on 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  269 

quartzite.  The  proximity  of  the  sheared  and  otherwise  greatly 
deformed  dove-colored  limestone  and  its  associated  rock  just  east 
of  Mt.  Anthony,  south  of  Bennington  town,  to  interbedded 
rocks  practically  contiguous  with  them  on  the  east,  certainly 
suggests  overlap  such  as  is  found  and  more  plainly  seen  at  the 
north.  In  the  imaginary  elevation  of  the  interbedded  rocks  of 
the  valley  along  the  western  portion  south  of  Bennington,  ap- 
parently beneath  them  would  be  carried  upward  some  younger 
rock  which  had  been  overlapped  by  them.  The  conditions  so 
far  imagined  give  us  apparently  old  rock  resting  against  younger 
rock  along  a  reverse  fault  and  a  thrust  plane.  Perhaps  on  the 
principle  of  differential  normal  faulting  in  the  region,  the  Mt. 
Anthony  ridge  would  have  to  be  elevated  somewhat  in  this  process 
of  restoration.  The  crystalline  limestones  and  marbles  underly- 
ing Mt.  Anthony  are  relatively  undeformed  internally,  presenting 
in  their  clearly-bedded  condition  a  contrast  to  the  marbles  farther 
north ;  they  are  highly  crystalline,  but  to  a  •  large  extent  not 
mashed  and  crushed.  Directly  east  of  them  the  bluish-gray 
limestone  and  its  gray  associate  are  greatly  deformed  internally, 
largely  through  shearing  and  brecciation.  It  would  appear  that 
this  evidence  of  compression  with  the  general  field  relations  could 
be  taken  to  mean  that  there  had  been  a  movement  of  one  rock 
mass  on  another  and  the  two  masses  which  seemingly  would  have 
been  involved  are  the  marbles  of  Mt.  Anthony  and  the  sheared 
rocks  just  east  of  them.  The  marbles  are  presumably  younger 
than  the  other  rocks.  Walcott  found  certain  fossils  (Trenton) 
which  would  seem  to  indicate  such  a  probability ;  the  writer  found 
certain  fossils  which  indicate  Chazy  age  for  the  sheared  rocks 
(see  above).  The  Chazy  has  apparently  broken  and  ridden  up- 
ward on  the  Trenton  along  a  reverse  fault  plane  now  marked  by 
the  rather  extended  zone  of  strong  brecciation  south  of  Benning- 
ton. 

The  marbles  of  Mt.  Anthony  are  capped  by  schist  or  phyl- 
lite.  Along  the  ridge  southward  near  Carpenter  Hill  the  rocks 
along  the  summit  and  eastern  slope  are  interbedded  black  phyllite, 
sericite  schist  and  quartzite.  Along  a  scarp  which  extends  from 
Carpenter  Hill  nearly  to  Pownal  Center  these  terrigenous  rocks, 
for  some  of  the  distance  at  least,  rest  against  the  interbedded 
series  of  the  Lower  Cambrian.  South  of  Pownal  Center  the 
surface  rocks  of  the  ridge  are  largely  crushed  black  phyllites, 
often  pyritiferous,  or  chlorite-sericite  schist.  The  schist  mass 
bends  southeasterly  and  cuts  across  the  strike  of  the  interbedded 
and  other  rocks  northward,  finally  abutting  against  the  massive, 
granular  quartzite  of  the  plateau. 

West  of  Carpenter  Hill  is  the  crushed  limestone  of  North 
Pownal  with  some  sheared,  bluish  or  dove-colored  rock  along  the 
eastern  part  of  the  mass.  On  this  limestone  and  jammed  in  with 
it  is  the  black,  pyritiferous  phyllite,  the  same  rock  that  surrounds 


270  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

it.  Between  Carpenter  Hill  and  the  limestone  hill  at  North 
Pownal  are  areas  in  which  patches  of  phyllite  and  limestone  are 
intermingled  at  the  present  surface.  In  North  Pownal  the  lime- 
stone rests  on  the  schist ;  it  does  also  west  of  the  Hoosic  River, 
north  of  Pownal  station.  The  field  relations  all  about  speak  with 
emphasis  of  former  strong  compression  of  the  region. 

Reckoning  with  the  idea  of  an  overlap  of  Ordovician  cal- 
careous rocks  on  an  old  Cambrian  surface,  as  developed  in  con- 
nection with  apparent  relations  at  the  north,  and  with  the  evi- 
dence of  severe  compression  which  is  everywhere  manifest,  the 
present  relations  seem  to  be  capable  of  at  least  partial  explanation. 
It  would  seem  that  except  for  normal  faulting  their  relations 
must  recognize  deformation  by  powerful  compression  and  that 
the  structural  characters  of  the  rocks  show  that  deformation  took 
place  largely  in  the  "zone  of  fracture."  The  evidence  is  good  that 
many  of  the  rock  masses  have  come  to  be  where  they  are  now 
as  the  result  of  disturbance  by  rupture  and  displacement. 

The  interbedded  terrigenous  rocks  on  Carpenter  Hill  are 
counterparts  of  similar  rocks  on  which  the  Ordovician  limestones 
rest  in  the  northern  part  of  the  Taconic  hill  region.  The  schist 
of  Mann  and  Mason  hills,  except  for  its  more  abundant  chlorite, 
is  like  that  of  West  Mountain.  The  dove-colored  rock  and  its 
gray  dolomite  are  like  those  in  Benson  and  OrAvell,  except  for 
greater  metamorphism ;  they  are  much  like  those  in  Brandon. 

Proceeding  with  the  strong  feehng  that  has  come  from  actual 
and  extensive  examination  of  the  whole  region  it  seems  that  the 
Bennington  area  does  not  dififer  essentially  from  other  areas  of 
the  Taconic  hills  near  the  Vermont  valley  that  have  been  dis- 
cussed. It  appears  that  under  compression  the  rocks  of  the 
region  were  broken  by  reverse  faults.  It  would  seem  that  the 
members  of  the  Lower  Cambrian  series  were  displaced  with 
reference  to  each  other  and  that  the  members  of  the  overlying 
Ordovician  rocks  were  also  displaced  with  reference  to  each 
other.  It  seems  possible  to  imagine  that  the  quartzite-schist  mass 
was  either  ruptured  without  much  folding  or  that  it  was  folded 
and  overturned  and  then  ruptured.  The  marbles  of  Mt.  Anthony 
were  protected  from  pronounced  deformation  by  a  great  fracture, 
probably  a  reverse  fault,  that  cut  up  through  them.  At  Carpenter 
Hill  and  southward  the  crush  zone  apparently  dies  away.  The 
quartzite-schist  mass  was  apparently  either  folded  and  overturned 
or  ruptured  and  pushed  up,  perhaps  both.  The  calcareous  rocks 
of  North  Pownal  were  caught  and  mashed  and  the  schist  jammed 
in  with  them  and  carried  over  them ;  it  was  also  apparently, 
carried  over  Mt.  Anthony.  On  the  basis  of  restoration,  the 
Lower  Cambrian  calcareous  rocks  may  once  have  overlapped  the 
rocks  that  formerly  lay  on  the  Mt.  Anthony  ridge.  In  testing  the 
validity  of  the  interpretation,  one  must  recall  contrasts  in  the 
different  rocks  with  reference  to  metamorphism.     The  schist  and 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  271 

for  the  most  part  the  Ordovician  calcareous  rocks  were  subjected 
to  conditions  different  from  those  within  the  mass  that  over- 
rode them.  The  probabihty  of  overlap  by  lateral  thrust  is  strong, 
on  the  basis  of  what  is  known  farther  north,  but  its  extent  is 
wholly  uncertain.  All  thrust  relations  have  been  thoroughly  dis- 
guised by  normal  faulting.  Whether  any  of  the  Ordovician 
calcareous  rock  has  been  much  displaced  by  lateral  thrust  it  is 
not  possible  to  tell. 

North  of  North  Bennington  we  find  the  counterpart  of  the 
dove-colored  rock  which  occurs  south  of  Bennington,  and  which 
seems  to  be  Chazy,  resting  on  the  phyllite,  although  greatly  de- 
formed. Whether  this  rock  is  substantially  in  place  it  is  not  pos- 
sible to  decide.  On  the  basis  of  a  restoration  it  would  be  lifted 
to  some  extent  and  might  come  to  the  level  of  similar  rock  now 
found  on  the  southern  slopes  of  West  Mountain.  Erosion,  as 
well  as  faulting,  have  operated  to  obscure  relations  here. 

It  is  still  maintained  that  by  a  combination  of  reverse  fault- 
ing and  lateral  thrusting,  a  portion  of  the  floor  on  which  the  Or- 
dovician rocks  apparently  lie,  whether  by  deposition  or  otherwise, 
could  be  carried  over  the  limestone  and  perhaps  give  the  appear- 
ance of  being  something  very  different  from  what  it  really  is. 

Regarding  apparent  conf ormability ;  this  might  be  simulated. 
Logan  has  distinctly  called  attention  to  the  superposition  of  cer- 
tain rocks  on  others  which  seem  to  be  conformable,  but  which 
give  the  strongest  possible  impression  of  being  very  different  in 
age  and  speaks  of  the  probable  greater  age  of  those  which  are 
superior  in  position.  .  . 

There  is  apparently  nothing  which  requires  that  a  thrust 
plane  should  cut  in  any  particular  way  through  the  rocks  that 
are  interposed,  so  to  speak,  in  its  path  except  a  variable  resist- 
ance. It  might  have  undulated  in  the  most  irregular  fashion  at 
some  places  and  have  been  fairly  regular  at  others.  At  times  it 
might  have  passed  from  a  horizontal  direction  to  one  nearly  ver- 
tical, and  might  have  cut  downward  as  well  as  upward.  In  cases 
where  patches  of  limestone  rest  on  a  schist,  which  in  turn  rests  on 
a  marble  presumably  by  minor  thrust  and  where  all  are  overlapped 
by  thrust,  it  is  possible  to  imagine  that  these  patches  either  repre- 
sent rock  that  is  where  it  was  before  overlap  by  a  thrust  which 
cut  above  them,  or  that  it  has  been  carried  there  by  the  thrust 
cutting  down  into  limestones  farther  east  and  moving  some  of  that 
rock  with  the  overriding  mass.  They  would  belong  in  a  different 
category  in  one  case  from  what  they  would  in  the  other,  being 
simple  or  displaced  erosion  outliers  in  the  former  case  and  thrust 
erosion  outliers  in  the  latter.  The  question  of  the  extent  to  which 
thrusts  may  have  moved  masses  of  Ordovician  limestone  or  mar- 
ble, small  or  large,  it  is  of  course  impossible  to  decide.  The 
possibility  apparently  needs  to  be  recognized. 


272  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

North  of  Brandon  the  thrust  apparently  did  not  raise  Cam- 
brian schist  and  push  it  on  marble,  but  only  the  interbedded  series 
was  thrust  on  the  marble. 

Northward  it  may  be  that  the  thrust  along  the  western  edge 
of  the  plateau  disappears  and  that  there  is  only  one  thrust  plane. 
The  eastern  thrust  at  the  south  may  be  a  minor  one  compared 
with  that  which  drove  the  Lower  Cambrian  rocks  and  their  load 
over  the  "Utica,"  and  possibly  may  have  been  of  widely  different 
date. 

It  is  interesting  to  note  that  apparently  nowhere  west  of  the 
plateau  and  east  of  the  margin  of  the  thrust  as  now  developed 
by  erosion  along  Lake  Champlain  or  in  the  Laconic  hills  has  the 
base  or  basement  of  the  presumably  Lower  Cambrian  been  ex- 
posed. 

In  the  early  stages  of  the  deformation  which  was  to  cul- 
minate in  lateral  overlapping  thrusts  of  the  Cambrian  rocks,  the 
whole  floor  of  these  rocks  and  their  overlying  load  under  the 
tremendous  compression  were  probably  folded  and  crumpled. 
There  were  probably  developed  many  reverse  faults  of  varying 
throw,  some  of  which  were  probably  very  small.  At  this  time 
the  rocks  undoubtedly  also  were  strongly  sheared.  Schistose 
structure  was  developed  in  the  impure  muds,  cleavage  in  the  slates, 
and  folds  and  ruptures  in  the  quartzites.  Similar  deformations 
were  produced  in  the  overlying  limestones. 

The  dates  of  these  displacements  may  only  be  conjectured. 
In  view  of  the  apparent  nature  and  magnitude  of  the  regional 
deformation  one  cannot  be  sure  that  some  later  Paleozoic  strata 
may  not  have  once  been  present  in  the  region. 

At  some  post-Ordovician  period  the  strata  were  cut  by  dikes 
of  igneous  rock,  which  in  many  places  cut  through  the  displaced 
rocks  from  the  substratum  beneath.  So  far  as  the  writer  knows, 
there  is  no  evidence  that  sets  the  date  of  the.  intrusion  and  it 
may  have  been  post-Carboniferous. 

It  is  not  easy  to  discern  how  much  deformation  of  the  thrust 
planes  by  folding  occurred  subsequent  to  their  formation.  East 
of  Brandon  the  apparent  plane  of  overlap  of  the  interbedded 
series  of  the  Cambrian  does  not  seem  to  have  been  much  de- 
formed. Irregularities  in  thrust  planes,  which  are  more  prob- 
ably irregular  than  regular  at  the  outset,  by  subsequent  compres- 
sion of  the  region  seemingly  would  not  be  easy  to  see.  If  the 
thrusts  were  of  pre-Devonian  date  it  seems  as  though  there  would 
be  more  evidence  than  is  apparent  of  subsequent  deformation  in 
the  Appalachian  folding  of  post-Carboniferous  time.  The  prob- 
ability of  a  late  date  for  the  big  thrusts  on  this  basis  grows 
stronger. 

The  presence  of  thrusts  in  the  region  on  the  scale  that  has 
been  described  in  part  and  postulated  in  part  greatly  complicates 
the  question  of  the  character  and  extent  of  any  folding  that  has 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  273 

been  assumed  to  have  occurred  at  the  close  of  Ordovician  time 
in  this  region.  The  assignment  of  date  to  the  structural  features 
of  the  rocks  of  a  region  like  that  of  western  Vermont  depends 
upon  one's  viewpoint. 

It  seems  reasonably  clear  that  at  some  time  subsequent  to 
the  production  of  the  major  features  of  the  region  that  are  due 
to  compression,  there  came  a  period  of  extensive  deformation  by 
normal  faulting.  It  would  seem  that  it  was  at  this  time  that  the 
structural  outlines  of  what  are  now  the  Vermont  valley  and 
Champlain  lowland  were  formed.  Between  what  is  now  the 
western  edge  of  the  Green  Mountain  plateau  and  the  region  now 
represented  by  the  Taconic  range,  the  rocks  were  dropped,  pro- 
ducing a  great  structural  trough.  Northward  was  formed  the 
outlines  of  the  Champlain  lowland  between  the  plateau  on  the 
east  and  the  Adirondacks  on  the  west.  Considering  the  down- 
faulted  region  as  a  whole  the  movement  was  differential  and 
involved  flexures  as  well  as  actual  ruptures.  The  date  at  which 
this  deformation  occurred  again  can  only  be  conjectured.  Pos- 
sibly it  occurred  at  the  time  when  similar  deformations  outlined 
the  great  Triassic  troughs  of  our  Atlantic  border. 

It  seems  not  unlikely  that  during  the  time  of  post-Triassic 
faulting_in  the  eastern  part  of  the  country  there  might  have  been 
renewed  disturbance  of  this  general  region  and  that  some  of  the 
fault  lines  now  marked  by  scarps  in  the  Taconic  hills  and  else- 
where may  belong  to  this  period  of  disturbance.  Such  displace- 
ments are  not  to  be  confused,  however,  with  reverse  faults.  It 
is,  however,  often  not  possible  to  decide  whether  certain  obvious 
displacements  between  interbedded  quartzites  and  phyllites  of  the 
Taconic  hills  are  reverse  or  normal  faults. 

Some  of  the  displacements  along  Lake  Champlain  which  have 
been  regarded  as  reverse  faults  or  thrusts  and  are  marked  by 
scarps  are  apparently  really  normal  faults  within  thrusted  masses. 
The  margin  of  the  thrust  is  really  at  a  distance  from  the  scarps 
in  question.  For  example,  the  displacements  on  the  west  of 
Snake  and  Buck  mountains  and  west  of  the  Orwell  and  Benson 
hills  are  probably  normal  faults  cutting  through  a  great  lateral 
thrust.  These  masses  were  covered  at  one  time  and  have  been 
exposed  by  erosion.  They  stand  higher  now  than  the  rocks  at 
the  west  of  them  because  the  latter  were  dropped  and  the  quartz- 
ite  was  carried  downward  beneath  them.  The  thrusts  extended 
west  of  these  scarps  an  indeterminate  distance,  and  apparently 
often,  if  not  usually,  across  the  lake,  at  least. 

There  is  apparently  nothing  definite  in  the  region  to  tell 
whether  any  of  the  thrusts  were  the  results  of  previous  erosion. 
It  is  true  that  east  of  Brandon  and  at  other  places  the  inter- 
bedded series  lies  on  the  marble  and  it  is  probable  that  other 
Cambrian  rocks  lie  on  marble ;  but  it  seems  conceivable  that  these 
conditions  could  have  been  produced  even  though  there  were  a 


274  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

mass  of  rocks  above  the  limestones  now  represented  by  the  mar- 
bles by  reason  of  the  way  the  thrust  plane  could  have  cut  through 
the  mass. 

It  is  not  necessary  that  we  should  assume  that  the  marbles 
were  not  covered  by  other  rocks  when  these  thrusts  occurred. 
Such  has  not  intentionally  been  the  argument;  the  explanation 
of  the  particular  kind  of  terrigenous  rock  that  now  covers  the  mar- 
ble at  places  is  apparently  one  problem  to  be  solved.  A  great 
shear  seemingly  might  have  been  as  effective  as  erosion  in  trun- 
cating a  folded  series.  This  statement  would  seem  to  apply  gen- 
erally and  to  fit  the  conditions  along  the  lake  as  well  as  those  near 
the  plateau. 

The  present  physiography.  It  has  been  a  widely-accepted 
theory  that  during  middle  and  late  Mesozoic  time  a  large  por- 
tion of  the  Atlantic  border  of  our  country  was  reduced  by  the 
forces  of  subaerial  erosion  to  a  great  peneplaned  region,  and 
that  in  succeeding  Tertiary  time  the  region  was  elevated  by  an 
extensive  warping  movement.  According  to  this  theory  the 
present  physiography  is  to  be  explained  as  the  result  of  the  re- 
newed action  of  the  base-levelling  agencies  as  the  region  was 
gradually  elevated.  For  certain  regions  it  does  not  appear  that 
any  better  theory  has  been  advanced  to  explain  the  present  con- 
ditions within  them. 

Accepting  this  view,  the  present  physiographic  outlines  of 
western  Vermont  apparently  must  have  been  shaped  along  lines 
that  had  been  determined  by  the  great  deformations  which  the 
region  had  suffered.  The  rocks  in  the  different  parts  of  western 
Vermont,  whether  the  region  was  one  of  early  folding  and  much 
later  thrusts  or  one  of  folds  and  thrusts  independent  of  pro- 
nounced earlier  deformation,  had  been  brought  into  such  relative 
positions  that  during  late  Mesozoic  time,  allowing  for  some  ero- 
sion, there  was  produced  much  the  same  relation  that  we  see 
today  from  west  to  east  across  the  State :  a  great  truncation  of 
perhaps  lofty  masses  and  exposure  of  rocks  of  one  age  here  and 
another  there.  We  note  the  oldest  rocks  at  the  east  and  the 
youngest  at  the  west,  as  far  as  exposure  has  gone.  The  structural 
outlines  of  the  Vermont  valley  and  Champlain  lowland  had  pre- 
sumably already  been  laid  down  by  the  downfaulting  of  great 
blocks  of  soft  rocks  between  masses  of  more  resistant  crystallines. 
Although  all  were  alike  presumably  reduced  to  a  peneplain  in 
late  Cretaceous  time,  upon  later  elevation  the  forces  of  erosion 
discovered  the  downfaulted  masses  of  softer  rocks  and  wore 
them  rapidly  away. 

The  present  physiography  of  the  region  gives  some  hints 
of  the  deformations  which  it  has  undergone,  and  a  gross  surface 
section  across  the  State  adds  something  more ;  but  it  must  be  ap- 
parent that  the  physiography  by  itself  is  wholly  insufficient  to 
explain  the  complicated  structure  of  the  rocks  of  western  Ver- 
mont. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  275 

SUPPLEMENTAKT  NOTE. 

Some  of  the  names  in  this  paper  designating  fossils  from  exposures 
studied  by  the  writer  are  used  chiefly  as  general  descriptive  terms  for 
forms  whose  identities  the  nature  of  the  material  would  often  make  it 
difficult  to  establish.  As  indices  to  the  horizons  of  the  containing  rocks 
their  values  have  been  recognized  in  many  instances  by  reason  of  con- 
comitant features,  such  as  reasonably  apparent  stratigraphic  associa- 
tions with  other  rock  whose  identity  could  seemingly  be  more  conclu- 
sively fixed,  and  from'  occurrence  in  similar  rocks  at  other  places  in  the 
same  region  with  other  and  different  fossils  whose  identities  were 
more  obvious.  Particularly  among  terms  used  for  such  general  descrip- 
tive purposes  the  names  Pleurotomaria  and  Murchisonia  were  applied  to 
markings  which  strongly  resemble  either  some  of  the  species  of  Pleuro- 
tomaria or  some  of  those  of  Murchisonia  as  described  in  the  older 
literature  to  which  the  general  reader  probably  would  most  likely  first 
refer,  such  as  the  Paleontology  of  New  York  by  James  Hall,  or  early 
publications  of  the  Geological  Survey  of  Canada  by  Billings,  as  well  as 
the  early  descriptions  of  the  formations  of  Vermont.  Most  of  the  forms 
assigned  to  Murchisonia  by  earlier  writers  are  now  referred  to  other 
genera  (Lophospira,  Eormotoma,  etc.),  and  the  same  is  true  for  Pleuro- 
tomaria. 

Other  names  which  have  been  used  in  reference  to  fossils  are 
obviously  citations  from  the  literature  and  in  such  connection  are 
employed  without  presuming  to  pass  upon  their  validity  or  synonymy. 

Certain  other  names  have  been  employed  also  because  of  their  use 
by  others  with  reference  to  Vermont  formations  in  describing  certain 
characteristic  fossils  and  in  making  comparison  thereby  with  rocks  of 
other  regions.  In  such  cases  attempt  has  not  usually  been  made  to 
establish  with  absolute  positiveness  just  what  names  in  the  latest 
synonymy  of  Ordovician  fossils  should  apply  to  the  forms  referred  to. 
In  the  list  given  beyond  certain  probabilities  are  indicated. 

The  general  structure  of  the  region  suggests  that,  so  far  as  preserva- 
tion of  fossils  in  certain  disturbed  and  somewhat  metamorphosed  strata 
permits,  it  may  prove  desirable  to  undertake  studies  designed  to  draw 
comparisons  among  fossils  of  different  localities  and  rocks  in  the  gen- 
eral Champlain  region  in  order  to  obtain  further  light  on  the  probable 
extent  of  the  thrust  deformations  which  the  region  has  obviously 
suffered,  and  to  ascertain  if  any  peculiar  or  anomalous  faunal  features 
exist  in  the  region  which  could  be  ascribed  to  such  disturbances  as  the 
foregoing  paper  has  discussed. 

It  may  perhaps  be  said  that  the  older  names  have  an  historical 
value  in  tracing  the  progress  of  knowledge  of  the  rocks  of  western 
Vermont;  but  better  knowledge  of  the  exact  affinities  of  the  fossils 
is  doubtless  required  before  the  ancient  geographic  relations  of  those 
rocks  may  be  fully  understood. 


276 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


Name  used. 


Bellerophon  sp. 

Ophileta  complanata,  Vanuxem. 


Maclurea  magna,  Emmons. 
Strephochaetus  sp. 

Trinucleus  concentricus, 
{Trinucleus  concentrica  of  various 

authors). 
Graptolithus  pristis. 


Prasopora  sp. 


Possible  oe  probable  emendation. 


Probably      Sinuites      cancellatus, 

Hall. 
Possibly   equivalent   to   som-e   one 

of    the    forms    described    as    0. 

compacta,  Salter. 
Maclurites  magnus.   Lesueur. 
Girvanella,       probably       ocellata, 

Seely. 
Cryptolithus  tesselatus,  Green. 


Graptolithus  pristis,  Hall. 

(Possibly  Diplograptus  sp.  or 
Glossograptus  sp.) 

P.  simulatrix,  var.  orientalis, 
Ulrich. 

(Some  specimens  collected  by  the 
writer  at  South  Hero  were  ex- 
amined by  Dr.  Ruedemann  of 
Albany  in  connection  with 
studies  of  Trenton  fossils  from 
Grand  Isle  and  identified  as  P. 
simulatrix,  var.  orientalis,  Ulr.^ 
In  view  of  the  recognition  of 
this  form  in  the  Champlain  val- 
ley the  writer  prepared  radial 
and  tangential  sections  of  speci- 
mens collected  by  him  at  the 
grist  mill,  one  mile  west  of  Or- 
well village,  and  on  the  lake 
shore  in  Orwell  just  north  of  the 
Benson  line,  and  compared  with 
the  descriptions  and  figures 
given  by  Ulrich  in  the  Geology 
of  Minnesota,  vol.  3,  part  1, 
1895,  pp.  245-248,  plate  16,  and 
found  his  specimens  also  to  be 
P.  simulatrix,  var.  orientalis, 
Ulr.) 


1  Personal  communication. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  277 

BIBLIOGRAPHY. 

1845 — Adams,  C.  B.  First,  Second,  Third  and  Fourth  Annual  Reports 
on  the  Geology  of  Vermont. 

1846 — Emmons,  E.     Agriculture  of  New  York. 

1861 — Hitchcock,  E.,  and  Others.     Geology  of  Vermont,  2  vols. 

1861 — Baeeande,  J.,  Logan,  Sir  W.,  Hall,  James.  Correspondence  on 
the  Taconic  System  and  the  age  of  the  Fossils  found  in  the 
Rocks  of  Northern  New  England  and  the  Quebec  Group  of 
Rocks.    Amer.  Jour.  Sci.     Vol.  31. 

1861 — Baebande,  J.  Documens  Anciens  et  Nouveaux  sur  la  Primordiale 
et  le  Systeme  Taconique  en  Amerique.  Bull.  Soc.  Geol.  de 
France.     Vol.  2. 

1863 — Logan,  Sir  W.  E.     Geology  of  Canada,  Text  and  Atlas. 

1877 — Dana,  J.  D.  An  Account  of  the  Discoveries  in  Vermont  Geology 
of  the  Rev.  Augustus  Wing.     Amer.  Jour.  Sci.     Vols.  13  and  14. 

1877 — Dana,  J.  D.  On  the  Relations  of  the  Geology  of  Vermont  to  that 
of  Berkshire.     Amer.  Jour.  Sci.     Vol.  14. 

1879— Dana,  J.  D.  On  the  Hudson  River  Age  of  the  Taconic  Schists. 
Amer.  Jour.  Sci.     Vol.  17. 

1880— Dana,  J.  D.  Note  on  the  Age  of  the  Green  Mountains.  Amer. 
Jour.  Sci.     Vol.  19. 

1882 — Dana,  J.  D.  The  Geological  Age  of  the  Taconic  System.  Quart. 
Jour,  of  the  Geol.  Soc.    Aug.,  1882. 

1884 — Geikie,  a.,  Peach,  B.  N.,  and  Horne,  J.  The  Crystalline  Rocks 
of"  the  Scottish  Highlands.     Nature.     Vol.  31. 

1884 — Dana,  J.  D.  On  the  Southward  Ending  of  a  Great  Synclinal  in 
the  Taconic  Range.     Amer.  Jour.  Sci.     Vol.  28. 

1885— Ford,  S.  W.  Great  Fault,  Schodack  Landing,  N.  Y.  Amer.  Jour. 
Sci.     Vol.  29. 

1885 — Dana,  J.  D.  On  Taconic  Rocks  and  Stratigraphy,  with  a  Geolog- 
ical Map  of  the  Taconic  Region.  Amer.  Jour.  Sci.  Vol.  29. 
See  also  Vol.  33,  1887. 

1886— McCoNNELL,  R.  G.  Report  on  the  Geological  Features  of  a  Por- 
tion of  the  Rocky  Mountains.  Ann.  Rept.  Geol.  Surv.  Can. 
Vol.  2. 

1886 — Dana,  J.  D.  Berkshire  Geology.  A  paper  read  before  the  Berk- 
shire Historical  and  Scientific  Society,  Pittsfield,  Mass.,  Feb.  5, 
1885. 

1886 — Brainerd,  E.  and  Seely,  H.  M.  Notice  of  Geological  Investiga- 
tions along  the  Eastern  Shore  of  Lake  Champlain.  Bull.  Amer. 
Mus.  Nat.  Hist.     Vol.  1. 

1888 — Peach,  B.  N.,  Horne,  J.,  Gunn,  W.,  Clough,  C.  T.,  Hinxman,  L., 
Cadell,  H.  M.  Communicated  by  Geikie,  A.  Report  on  the 
Recent  Work  of  the  Geological  Survey  in  the  North-West 
Highlands  of  Scotland.     Quart.  Jour,  of  the  Geol.  Soc.    Vol.  44. 

1888 — Walcott,  C.  D.  The  Taconic  System  of  Emmons  and  the  Use  of 
the  Name  Taconic  in  Geologic  Nomenclature.  Amer.  Jour.  Sci. 
Vol.  35. 

1888 — Dana,  J.  D.  A  Brief  History  of  Taconic  Ideas.  Amer.  Jour. 
Sci.     Vol.  36. 

1888 — Margerie  et  Heim.  Dislocations  de  I'ecorce  terrestre.  Zurich, 
1888. 

1888 — Eixs,  R.  W.  Second  Report  on  the  Geology  of  a  portion  of  the 
Province  of  Quebec.  Ann.  Rept.  Geol.  and  Nat.  Hist.  Survey 
of  Canada.     Vol.  3,  Part  2. 

1890 — Walcott,  C.  D.  The  Fauna  of  the  Lower  Cambrian  or  Olenellus 
Zone.     Tenth  Annual  Report  of  the  Director,  U.  S.  G.  S. 

1890 — Brainerd,  E.  and  Seely,  H.  M.  The  Calciferous  Formation  in  the 
Champlain  Valley.     Bull.  Amer.  Mus.  Nat.  Hist.     Vol.  3. 


278  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

1891 — Hayes,  C.  W.  The  Overthrust  Faults  of  the  Southern  Appala- 
chians.    Bull.  Geol.  Soc.  Amer.     Vol.  2. 

1891 — Bbaineed,  E.  The  Chazy  Formation  in  the  Champlain  Valley. 
Bull.  Geol.  Soc.  Amer.     Vol.  2. 

1891 — Wolff,  J.  E.  On  the  Lower  Cambrian  Age  of  the  Stockbridge 
Limestone.     Bull.  Geol.  Soc.  Amer.     Vol.  2. 

1891 — ^"Walcott,  C.  D.  Correlation  Papers,  Cambrian.  Bull.  U.  S.  G.  S. 
No.  8L 

1892 — WiLus,  Bailey.  The  Mechanics  of  Appalachian  Structure. 
Thirteenth  Annual  Rept.  of  the  Director,  U.  S.  G.  S.     Part  2. 

1892 — Van  Hise,  C.  R.  Correlation  Papers,  Pre-Cambrian.  Bull.  U.  S. 
G.  S.    No.  86. 

1893 — Dakton,  N.  H.  On  two  Overthrusts  in  Eastern  New  York.  Bull. 
Geol.  Soc.  Amer.     Vol.  4. 

1893 — Willis,  B.  and  Hayes,  C.  W.  Conditions  of  Appalachian  Fault- 
ing.    Amer.  Jour.  Sci.     Vol.  46. 

1893 — FoEESTE,  A.  F.  New  Fossil  Localities  in  the  Early  Paleozoic. 
Amer.  Jour.  Sci.     Vol.  46. 

1893 — Dale,  T.  Nelson.  On  the  Structure  of  the  Ridge  between  the 
Taconic  and  Green  Mountain  Ranges  in  Vermont.  Fourteenth 
Ann.  Rept.  of  the  Director,  U.  S.  G.  S.     Part  2. 

1894 — PuMPELLY,  R.,  Wolff,  J.  E.,  and  Dale,  T.  N.  Geology  of  the 
Green  Mountains  in  Massachusetts.  Monograph  U.  S.  G.  S. 
No.  23. 

1894 — Whittle,  C.  S.  Algonkian  Rocks  in  Vermont.  Jour.  Geol. 
Vol.  3. 

1895 — Dale,  T.  N.  Structural  Details  in  the  Green  Mountain  Region 
and  in  Eastern  New  York.  Sixteenth  Ann.  Rept.  of  the  Director 
U.  S.  G.  S.     Vol.  4,  Part  1. 

1895 — Van  Hise,  C.  R.  Principles  of  North  American  Pre-Cambrian 
Geology.  Sixteenth  Ann.  Rept.  of  the  Director  U.  S.  G.  S. 
Vol.  4,  Part  1. 

1896 — Bbaineed,  E.  and  Seely,  H.  M.  The  Chazy  of  Lake  Champlain. 
Bull.  Amer.  Mus.  Nat.  Hist.     Vol.  8. 

1898 — Dale,  T.  Nelson.  The  Slate  Belt  of  Eastern  New  York  and 
Western  Vermont.  Nineteenth  Ann.  Rept.  of  the  Director 
U.  S.  G.  S.     Part  3. 

1899 — Emeeson,  B.  K.  The  Geology  of  Eastern  Berkshire  County, 
Mass.  Bull.  U.  S.  G.  S.  No.  159. 

1899 — 'White,  Theodobe  G.  Upper  Ordovician  Faunas  in  Lake  Cham- 
plain Valley.     Bull.  Geol.  Soc.  Amer.     Vol.  10. 

1901 — ^RuEDEMANN,  R.  Hudson  River  Beds  near  Albany  and  their 
Taxonomic  Equivalents.     N.  Y.  State  Mus.  Bull.  No.  42. 

1902 — Willis,  Bailey.  Stratigraphy  and  Structure,  Lewis  and  Livings- 
ton Ranges,  Montana.     Bull.  Geol.  Soc.  Amer.     Vol.  13. 

1902 — Peekins,  Geoege  H.  The  Geology  of  Grand  Isle.  Third  Report 
of  the  State  Geologist. 

1904 — Dale,  T.  Nelson.  The  Geology  of  the  North  End  of  the  Taconic 
Range.     Amer.  Jour.  Sci.     Vol.  17. 

1905 — Raymond,  P.  E.  The  Fauna  of  the  Chazy  Limestone.  Amer. 
Jour.  Sci.    Vol.  19. 

1906 — Meeeill,  G.  p.  Contributions  to  the  History  of  American  Geol- 
ogy.    U.  S.  Nat.  Mus.  Report  for  1904,  No.  135. 

1906 — Edson,  G.  E.  Geology  of  St.  Albans  and  Vicinity.  Fifth  Report 
of  the  State  Geologist. 

1906 — Seely,  H.  M.  Beekmantown  and  Chazy  Formations  in  the 
Champlain  Valley.     Fifth  Report  of  the  State  Geologist. 

1907 — Keith,  Aethue.  Roan  Mountain  Folio.  Geological  Atlas  of  the 
U.  S.     No.  151. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  279 

1908 — Perkins,  Geokge  H.     Preliminary  Report  on  the  Geology  of  Chit- 
tenden County.     Sixth  Report  of  the  State  Geologist. 
1908 — Edson,  G.  E.     Geology  of  the  Town  of  Swanton.     Sixth  Report 

of  the  State  Geologist. 
1908 — Perkins,    George    H.     Preliminary    Report    on    the    Geology    of 

Franklin  County,  Vt.     Sixth  Report  of  the  State  Geologist. 
1909 — RuEDEMANN,  R.     Types  of  Inliers  Observed  in  New  York.     Bull. 

N.  Y.  State  Mus.     No.  133. 
1909 — Van   Hise,    C.   R.   and   Leith,   C.   K.     Pre-Cambrian   Geology   of 

North  America.     Bull.  U.  S.  G.  S.     No.  360. 
1909 — ScHUCHERT,   C.     Paleogeography  of  North  America.     Bull.   Geol, 

Soc.  Amer.     Vol.  20. 
1910 — Dale,  T.  N.     The  Cambrian  Conglomerate  of  Ripton  in  Vermont. 

Amer.  Jour.  Sci.     Vol.  30. 
1910 — Seely,  H.   M.     Preliminary  Report   on  the   Geology  of  Addison 

County.     Seventh  Report  of  the  State  Geologist. 
1910 — Perkins,    George    H.     Geology    of    the    Burlington    Quadrangle. 

Seventh  Report  of  the  State  Geologist. 
1910 — Kemp,  J.  F.  and  Ruedemann,  R.     Geology  of  the  Elizabethtown 

and  Port  Henry  Quadrangles.     Bull.  N.  Y.  State  Mus.     No.  138. 
1911 — Ulrich,  E.  O.     Revision  of  the  Paleozoic  Systems.     Bull.   Geol. 

Soc.  Amer.     Vol.  22. 
1911 — Gordon,   C.   E.    The   Geology  of  the  Poughkeepsie   Quadrangle. 

N.  Y.  State  Mus.  Bull.     No.  148. 
1912 — Willis,   Bailey.     Report  on  an  Investigation  of  the  Geological 

Structure  of  the  Alps.     Smithsonian  Miscellaneous  Collections. 

Vol.  56. 
1912 — Richards,  R.  W.  and  Mansfield,  G.  R.    The  Bannock  Overthrust. 

Jour.  Geol.    Vol.  20. 
1912 — Dale,   T.   Nelson.     The   Ordovician   Outlier   at  Hyde  Manor   in 

Sudbury.     Amer.  Jour.  Sci.     Vol.  33. 
1912— Dale,  T.  N.     The  Commercial  Marbles  of  Vermont.     Bull.  U.  S. 

G.  S.    No.  521.     See  also  Ninth  Report  of  the  State  Geologist, 

1914. 
1913 — Keith,  A.    Further  Discoveries  in  the  Taconic  Mountains.    Ab- 
stract.    Bull.  Geol.  Soc.  Amer.     Vol.  24. 
1913 — Dale,  T.  N.     The  Ordovician  Outlier  at  Hyde  Manor  in  Sudbury. 

Second  paper.     Amer.  Jour.  Sci.     Vol.  36. 
1914 — Gordon,  C.  E.     Notes  on  the  Geology  in  the  Vicinity  of  Benning- 
ton.    Ninth  Report  of  the  State  Geologist. 
1916 — Perkins,  George  H.     The  Geology  of  Western  Vermont.     Tenth 

Report  of  the  State  Geologist. 
1917 — Emerson,  B.  K.     Geology  of  Massachusetts  and  Rhode  Island. 

Bull.  U.  S.  G.  S.     No.  597. 


THE  GE0L06Y  OF  LAKE  WILL0U6HBY. 


Elbridge  C.  Jacobs, 
University  of  Vermont. 


Lake  Willoughby  lies  in  the  western  part  of  the  town  of 
Westmore,  near  the  eastern  boundary  of  Orleans  County,  and 
some  twenty-three  miles  north  of  St.  Johnsbury.  It  is  one  of 
the  most  beautiful  sheets  of  water  in  the  United  States  and  would 
not  suffer  by  comparison  with  the  Alpine  lakes  of  Switzerland. 
To  quote  from  Mr.  Walter  Crockett's  "Lakes  of  Eastern  Ver- 
mont," we  have  here  /'a  rare  combination  of  lake  and  mountain 
scenery,  a  lake  (five  miles  long  and  from  one-half  to  one  and 
one-fifth  miles  wide)  of  exquisite  loveliness  set  amid  bold  and 
rugged  mountains,  the  dark  tints  of  the  evergreen  forests  and  the 
delicate  silvery  whiteness  of  the  birches  being  reflected  as  in  a 
mirror  in  Willoughby's  deep  waters.  *****"  "Qn  either  side, 
at  the  southern  extremity  of  the  lake,  like  giant  guardians,  stand 
Mount  Pisgah  and  Mount  Hor,  with  their  Scriptural  names, 
keeping  watch  over  this  vision  of  scenic  loveliness."  The  slopes 
of  these  mountains  are  densely  wooded  save  where  erosion  re- 
veals nearly  vertical  cliffs  of  dark,  bronze-colored  rocks,  slashed 
with  bands  and  patches  of  a  lighter  material.  Below  the  cliffs 
are  enormous  talus  heaps  of  granite  and  other  material.  Rock 
falls  are  frequent,  a  fall  in  July  of  this  year  blocking  the  road 
for  several  days. 

The  lake  may  be  likened  to  the  section  of  a  giant  calabash 
gourd,  with  its  broad  end  lying  in  the  relatively  open  country  and 
its  curving  neck  penetrating  and  forming  a  gap  in  the  mountain 
range  at  its  southern  extremity.  The  lake  shores  were  formerly 
impassible  to  vehicles,  communication  between  the  eastern  and 
western  valleys  being  either  by  boat  or  else  by  a  mountain  road 
running  east  of  Mount  Pisgah.  But  some  sixty  years  ago  a 
road  was  built  along  the  eastern  (Mount  Pisgah)  shore  and  now 
forms  part  of  the  main  highway  between  St.  Johnsbury  and  New- 
port. Numerous  summer  cottages  and  the  Westmore  Hotel  are 
located  along  this  road  towards  the  northern  end  of  the  lake.  • 
"Westmore,"  a  girls'  camp,  was  built  in  1919  on  a  commanding 
hill  on  the  northwestern  shore.  The  camp  is  closed  this  season 
owing  to  financial  difficulties,  but  will  probably  be  reopened.     This 


r/. 


-/' 


"■  -t"^ 


,..^.... 


;-=?^'^ 
/ 


STUDIES  IN  THE  GEOLOGY  OF  WESTERN  VERMONT 

Second  Paper. 


Clarence  E.  Gordon, 
Massachusetts  Agricultural  College 


TABLE  OF  CONTENTS. 

Introduction. 

Descriptions  and  discussions  of  observations  made  by  the  writer  within 
the  Charaplain  lowland  and  adjacent  portions  of  the  Green  Moun- 
tain plateau. 
Grand  Isle  County. 

South  Hero  and  Grand  Isle. 

North  Hero. 

Alburgh. 

Isle  La  Motte. 
Franklin  County. 

Highgate. 

Swanton. 

St.  Albans. 

Georgia. 

Fairfax. 
Chittenden  County. 

Milton. 

Colchester. 

Essex. 

Burlington. 

South  Burlington. 

Williston. 

Shelburne  and  St.  George. 

Charlotte. 

Hinesburg. 
Addison  County. 

Ferrisburg  and   Vergennes. 

Monkton. 

Starkshoro. 

Panton. 

Waltham. 

New  Haven. 

Bristol,  including  parts  of  Lincoln. 

Addison. 

Weybridge. 

Middlebury. 

Bridport. 

Cornwall. 

Shoreham. 

Whiting. 

Salisbury. 

Leicester. 
General  Summary.  , 


144  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 


INTRODUCTION. 

A  description  of  the  principal  physiographic  divisions  of 
western  Vermont  and  a  general  statement  of  the  characters  dis- 
tribution and  certain  other  features  of  the  various  rock  formations 
found  in  those  divisions  may  be  found  in  the  first  paper  under 
this  title,  published  in  the  Twelfth  Report  of  the  State  Geologist. 
These  were  intended  to  serve  for  guidance  in  following  the  de- 
scription and  discussion,  offered  in  the  same  paper,  of  a  number 
of  observations  made  in  certain  parts  of  western  Vermont  which 
dealt  chiefly  with  the  deformations  of  the  different  rocks.  For 
the  present  paper,  which  gives  an  account  of  studies  of  the  field 
relations  of  the  rocks  in  other  parts  of  western  Vermont,  the 
general  statement  made  in  the  preceding  report  is  considered  sufifi- 
cient  and  need  not  be  repeated  nor  amplified  in  this  one. 

The  physiographic  divisions  mentioned  are  the  prominent 
ones  of  the  present  surface  of  this  part  of  the  state.  Each,  of 
course,  shows  many  minor  topographic  variations  incident  to  the 
character  and  structure  of  the  underlying  rock  and  the  modifying 
effects  of  erosion  and  other  agencies,  such  as  glaciation.  Except 
for  a  quarry  here  and  there  the  average  observer  is  probably 
impressed  only  by  the  grander  features  of  the  surface ;  it  is  their 
charm  that  invites  the  tourist  to  motor  through  this  part  of  Ver- 
mont or  impels  the  summer  resident  to  build  his  camp  on  some 
hill  or  mountain  side. 

So  conspicuous  indeed  are  these  larger  divisions  of  the  land- 
scape they  may  easily  impress  the  geological  student  as  possessing 
a  significance  beyond  that  which  they  really  have.  Geological 
accounts  of  different  parts  of  the  region  often  accentuate  these 
more  or  less  modern  features  and  it  seems  as  though  in  a  provin- 
cial treatment  of  them  their  true  geological  history  and  connec- 
tions have  been  more  or  less  obscured.  The  more  ancient  second- 
ary structural  features  of  the  rocks  bear  no  necessary  relation  to 
the  present  physiography  of  the  region,  which  is  due  in  part  to 
later  deformations  or  disturbances  and  in  part  to  repeated  erosion. 

Over  the  present  surface  of  western  Vermont  there  is  shown 
a  confusion  in  the  arrangement  of  the  rocks  that  is  very  baffling. 
This  confusion  is  very  clearly  due  in  large  measure  to  the  various 
deformational  and  metamorphic  changes  which  the  rocks  have 
suffered  and  to  certain  primary  features,  such  as  lateral  variations 
in  certain  members.  Added  to  these  are  the  effects  of  erosion 
and  glaciation.  Over  large  areas  correlation  may  not  be  made  by 
direct  aid  of  fossils,  and  one  must  rely  upon  other  criteria  of 
various  sorts.  Particular  mention  should  be  made  of  the  exten- 
sive mantle  of   surface  material,   either  bowlder  drift,   sand   or 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  145 

clay,  which  conceals  large  areas  and  imposes  great  difficulties  in 
working  out  the  structural  details  of  most  localities. 

The  student  who  confines  his  studies  to  a  small  portion  of 
the  region  may  gain  a  glimpse  of  the  nature  of  the  structure  of 
the  rocks  in  some  cases ;  in  'others  he  may  be  quite  confused.  It 
is  necessary  to  carry  one's  studies  over  a  wide  area  to  see  into 
the  plan  that  apparently  prevails  over  the  region  as  a  whole. 

The  studies  described  in  this  paper  and  the  earlier  one  were 
undertaken  in  the  hope  that  it  would  eventually  prove  possible  to 
examine  in  a  somewhat  critical  way  a  large  number  of  outcrops 
in  all  four  of  the  different  divisions  of  the  region,  which  the 
writer  has  defined,  with  the  purpose  of  getting  light  on  the  gen- 
eral plan  of  structure  of  the  rocks  and  in  order  to  discover  if  any 
marked  degree  of  unity  prevails  throughout.  For  reasons  that 
will  generally  be  understood  it  has  been  necessary  to  publish  ac- 
counts of  the  work  at  various  stages  of  its  progress.  At  this 
writing  there  still  remains  the  larger  portion  of  the  mass  of  rocks 
contained  within  what  is  known  as  the  Taconic  range,  which  is 
a  territory  which  the  writer  had  reserved  in  his  mind  for  future 
study.  From  studies  already  made  in  parts  of  the  range  it  seems 
likely  that  in  its  main  features  it  may  finally  be  reduced  to  a  plan 
of  structure  like  that  of  other  divisions  which  now  bear  little 
physiographic  resemblance  to  it.  Finally,  it  seemed  probable  that 
a  more  careful  inspection  than  has  yet  been  possible  could  be 
given  to  the  western  ranges  and  other  masses  of  the  Green  Moun- 
tain plateau  to  see  to  what  extent  the  rocks  now  lying  west  of 
the  plateau  could  be  traced  into  it  and  whether  the  deformations 
present  in  it  are  similar  in  plan  to  those  found  among  the  rocks 
now  lying  west  of  it.  Experience  has  served  to  show  that  ap- 
parently only  by  a  broad  survey  of  the  region  as  a  whole  is  it 
likely  that  one  may  grasp  the  true  significance  of  the  relations 
within  and  among  its  different  parts. 

The  general  similarity  shown  by  the  field  relations  in  widely 
separated  areas  indicates  a  fundamental  unity  of  structure  in  all 
of  them.  Moreover,  excursions  into  areas  contiguous  to  Vermont, 
such  as  western  Massachusetts  and  southern  Quebec,  as  well  as 
published  descriptions  for  other  adjoining  territory  and  for  dis- 
tricts still  more  remote  suggest  that  a  common  plan  of  structure 
may  prevail  over  a  much  wider  region  than  western  Vermont. 

The  work  and  writings  of  Professor  J.  D.  Dana,^  in  which  he 
aimed  to  show  the  relations  (general  similarity  or  unity  of  plan) 
between  the  geological  features  of  western  Vermont  and  those  of 
Berkshire  County,  Massachusetts,  and  other  areas  as  well,  are 
well  known.  The  writer's  conception  of  the  similarity  that  exists 
in  the  areas  described  by  Dana  follows  him  in  maintaining  that 

^  On   the   relations   of   the   Geology   of   Vermont  and   that   of   Berkshire, 
A.  J.  S.,  Vol.  XIV,  July,  1877. 


146  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

the  "western  half  of  the  whole  Green  Mountain  region  is  emi- 
nently a  natural  area,"  and  that  in  many  primary  features,  such 
as  general  age  and  general  original  interrelations,  the  rocks 
throughout  are  similar.  The  purpose  of  this  paper  is  to  indicate, 
if  possible,  the  kind  of  structure  in  which  western  Vermont  pos- 
sesses unity  and  to  show  the  apparent  nature  of  the  chief  deforma- 
tions which  have  disturbed  the  rocks.  Numerous  descriptions  of 
field  relations,  in  addition  to  those  given  in  the  first  paper,  will 
be  offered  to  show  the  dominant  influence  of  thrust  displacements 
of  various  magnitudes  and  of  kindred  phenomena  due  to  pressure 
acting  upon  highly  elastic  and  resistant  rock  formations  asso- 
ciated with  weaker  and  less  "competent"  strata. 

Extent  and  certain  other  features  of  the  region  described  in 
this  paper.  A  rough  estimate  of  the  dimensions  of  the  irregular 
territory  which  has  been  surveyed  gives  about  900  or  950  square 
miles.  It  includes  either  the  whole  or  large  portions  of  the  fol- 
lowing-named topographic  sheets  of  the  U.  S.  G.  S. : — Rouses 
Point,  St.  Albans,  Plattsburg,  Milton,  Willsboro,  Burlington,  Port 
Henry,  Middlebury,  Ticonderoga  and  Brandon.  In  a  north  to 
south  direction  it  extends  from  the  Canada  line  approximately  to 
the  southern  boundary  of  Leicester  in  Addison  County,  and  west 
to  east  from  the  New  York  State  boundary  to  the  western  margin 
of  the  Green  Mountain  plateau. 

The  ground  gone  over  has  not,  of  course,  all  been  studied  in 
minute  detail;  but  much  of  it  has  been  examined  with  more 
thoroughness  than  will  appear  in  the  descriptions,  in  the  search 
made  for  clues  of  different  sorts,  especially  for  fossils  in  the 
more  altered  rocks  found  in  the  eastern  portions  of  the  region. 

Some  parts  of  the  territory  have  been  described  more  or  less 
fully  in  the  first  paper ;  but  in  most  cases  these  areas  have  been  re- 
examined. 

The  lake  region  proper,  which  is  included  within  the  physi- 
ographic division  called  the  Champlain  lowland,  seems  to  call 
for  some  sort  of  specific  definition,  as  it  will  be  frequently  men- 
tioned in  the  following  pages.  In  addition  to  the  lake  with  its 
islands  there  are  along  its  border  many  areas  of  various  dimen- 
sions, often  small  but  again  of  considerable  size,  which  are  under- 
lain by  rocks  similar  to  those  which  form  the  islands  and  the  lake 
bottom.  Many  of  these  areas  are  now  covered  with  Champlain 
clays,  or  sands  brought  in  by  streams  entering  the  lake.  In  many 
places  outcrops  are  few,  especially  where  the  underlying  rock  is 
clearly  or  apparently  the  soft  shale  formation,  but  at  many  places 
limestone  beds  like  those  found  on  the  islands  project  above  the 
surface  deposits,  forming  knolls  and  ridges.  It  seems  likely  that 
if  the  clay  which  is  so  plentiful  over  portions  of  the  mainland 
near  the  lake  were  removed  these  areas  would  be  more  or  less 
inundated  by  the  lake  waters,  even  at  their  lower  levels,  and  that 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  147 

there  would  be  produced  a  very  different  shore  Hne,  more  numer- 
ous islands  and  a  larger  water  body.  A  similar  operation  on  the 
islands  would  in  some  cases  partition  them  into  smaller  units. 

Some  of  the  streams  which  enter  Lake  Champlain,  such  as 
Lewis,  Little  Otter  and  Otter  Creeks,  are  for  greater  or  less  dis- 
tances from  their  mouths  hardly  more  than  inundations  by  the 
lake  waters  of  narrow  channels  in  the  clays,  with  hardly  head 
enough  at  the  present  time  to  give  them  perceptible  currents ;  and 
Dead  Creek,  a  tributary  of  the  Otter,  is  practically  all  its  way 
a  sluggish  stream  of  this.  sort.  In  the  case  of  the  Otter  the 
inundation  extends  from  its  mouth  to  the  city  of  Vergennes, 
where  the  stream  tumbles  over  a  scarp  in  massive  dolomite  to  the 
graptolite  shales  below.  For  a  large  part  of  its  course  below 
Vergennes  the  river  flows  through  a  sand  plain  of  its  own  making 
and  at  its  mouth  it  has  formed  delta  levees  by  which  it  has  tied 
Fort  Cassin  to  the  mainland. 

Hog  Island,  so-called,  in  the  township  of  Swanton,  is  a  land- 
tied  island,  accomplished  in  this  case  by  the  delta  deposits  of 
the  Missisquoi  River. 

It  thus  appears  that  some  islands  have  become  secondarily 
attached  to  the  mainland  and  that  large  areas  of  the  mainland 
differ  from  the  lake  only  in  the  fact  that  clay  takes  the  place  of 
water.  Such  considerations  may  prove  helpful  to  the  reader 
when  in  the  succeeding  pages  different  areas  are  described  and 
compared  with  one  another. 

The  studies  which  were  described  in  previous  papers  were 
scattered  rather  generally  over  the  western  half  of  the  state 
and  were  conducted  in  much  more  detailed  and  systematic  manner 
in  some  places  than  in  others.  This  resulted  from  the  way  in 
which  the  general  problem  was  from  time  to  time  approached. 

The  rocks  first  examined  were  those  in  the  difficult  region 
around  Bennington,  in  the  southwestern  portion  of  the  state. 
Six  years  later  (1918)  a  trip  was  made  through  the  Vermont 
valley  and  parts  of  the  Champlain  lowland,  Taconic  range,  and 
Green  Mountain  plateau  with  the  definite  purpose  of  searching 
for  a  general  plan  of  structure  among  the  rocks  over  a  wide 
region  which  might  serve  as  a  key  to  the  relations  around  Ben- 
nington. Much  that  was  planned  for  this  trip  had  to  be  aban- 
doned on  account  of  illness.  In  the  seasons  of  1919  and  1920  a 
somewhat  systematic  study  was  made  of  a  wide  surface  section 
from  the  Green  Mountains  to  Lake  Champlain,  in  the  towns  of 
Brandon,  Sudbury  and  Orwell. 

From  these  several  studies,  especially  from  those  made  in 
Brandon,  Sudbury  and  Orwell,  various  inferences  were  drawn, 
some  of  which  were  given  a  broad  application  in  the  interpretation 
of  the  structure  of  the  region.  The  views  expressed  were  based 
on  personal  work.     Some  found  support  in  the  writings  of  other 


148  REPORT  OP  THE  AT'ERMONT  STATE  GEOLOGIST. 

workers  while  others  were  apparently  new  and  clearly  called  for 
such  substantiation  as  further  study  might  give. 

The  brief  studies  wdiich  it  had  been  possible  to  make  in 
various  parts  of  the  Champlain  lowland,  up  to  the  season  of  1921, 
had  tended  to  strengthen  the  belief  that  the  whole  of  western 
Vermont  is  "eminently  a  natural  area"  and  had  suggested  that 
the  lowland  would  probably  afford  the  field  relations  that  would 
serve  best  in  testing  certain  views  regarding  structure. 

The  Champlain  lowland  makes  up  a  large  portion  of  western 
Vermont.  It  merges  quite  imperceptibly  with  the  Vermont  valley, 
both  physiographically  and  geologically,  and  except  as  disguised 
by  certain  primary  differences  of  the  rocks  and  by  faulting  may 
reasonably  be  shown  to  merge  with  the  Taconic  range,  whose 
foothills  as  well  as  the  main  range  itself  still  show  vestiges  of  the 
features  that  are  now  best  preserved  over  the  lowland.  The  low- 
land then  seems  to  be  only  a  physiographic  subdivision  of  a  large 
region  whose  genetic  features  are  essentially  identical  throughout. 
Even  in  its  relation  to  the  Green  Mountain  plateau  the  designation 
of  lowland  should  not  be  understood  to  convey  the  idea  of  strong 
contrast  between  the  two,  for  over  long  distances  there  is  a  most 
gradual  transition  topographically  and  almost  complete  identity 
or  unity  geologically  between  adjacent  portions  of  them. 

Notwithstanding  these  recognizable  transitions  between  the 
lowland  and  the  higher  lands  of  the  Taconic  range  and  the  Green 
Mountain  plateau  and  the  presence  of  high  hills  at  many  places 
in  the  lowland  this  division  is  structurally  a  sunken  region  with 
respect  to  surrounding  higher  surfaces.  The  Vermont  valley 
may  be  viewed  as  the  southward  extension  of  the  lowland  between 
the  plateau  and  the  Taconic  range.  Since  in  its  breadth  from 
west  to  east  the  lowland  therefore  comprises  counterparts  of  the 
marginal  portion  of  the  plateau,  of  the  Vermont  valley  and  of  the 
Taconic  range  one  finds  within  it  relations  that  are  often  pre- 
served only  in  much  more  fragmentary  conditions  in  the  other 
divisions,  for  one  reason  or  other. 

The  meaning  of  the  comparisons  which  have  just  been  made 
of  parts  of  the  region  with  each  other  really  comes  out  only  after 
careful  field  study ;  but  it  is  hoped  that  the  discussions  which  will 
follow,  taken  with  those  which  were  given  in  the  first  paper,  will 
enable  the  reader  to  see  the  force  of  the  contention  that  difTerent 
parts  of  western  Vermont  possess  strong  similarities  in  a  number 
of  ways. 

A  survey  of  the  lowland  was  carried  on  during  the  seasons 
of  1921  and  1922,  together  with  some  study  of  the  marginal  por- 
tions of  the  plateau.  The  territory  covers  many  square  miles. 
It  was  necessary  to  confine  attention  to  those  field  relations  that 
bear  particularly  upon  structure,  simply  in  order  to  get  over  the 
ground  and  not  leave  untouched  any  large  number  of  places  that 


PLATE   XVIII 


^yj^-^'ST-^eT-......^^ 


2    PAr  ^^7i5^^>=-    '^   ^'^"'^ 


..v^rs'r^^^^^ 


W^     '^^'■ 


Township  map  of  Vermont. 


REPORT  OF  THE  VERMONT  STATE   GEOLOGIST.  ]49 

might  throw  Hght  on  the  main  problem.  Naturally  during-  the 
work  many  other  fascinating  problems  appeared  which  it  was 
necessary  to  pass  by. 

DESCRIPTIONS    AND    DISCUSSIONS     OF    OBSERVA- 
TIONS   MADE    BY    THE    WRITER    WITHIN    THE 
CHAMPLAIN   LOWLAND  AND  ADJACENT  POR- 
TIONS OF  THE  GREEN  MOUNTAIN  PLATEAU. 

General  plan  of  discussion.  As  the  field  studies  described 
herein  were  the  continuation  of  those  discussed  in  the  first  paper 
it  has  seemed  best  to  make  no  marked  change  in  mode  of  treat- 
ment. General  reference  will  be  given  by  counties  and  town- 
ships which  are  shown  on  the  accompanying  township  map  of 
Vermont.  Citations  of  localities  are  based  chiefly  on  the  topo- 
graphic quadrangle  sheets  of  the  United  States  Geological  Survey. 

It  may  prove  useful  in  some  cases  to  cite  observations  or  in- 
terpretations of  others  in  order  to  develop  the  writer's  viewpoint 
in  respect  of  relations  and  structure,  and  in  this  paper  this  will 
be  done  along  with  the  discussions  of  different  areas  rather  than 
in  the  form  of  a  general  preliminary  review,  such  as  was  given  in 
the  first  report. 

Because  there  is  often  a  close  relation  between  topography 
and  geology  the  topographic  features  that  are  of  interest  in, re- 
gard to  structure  will  be  mentioned  at  appropriate  places. 

GRAND  ISLE  COUNTY. 

Townships  of  South  Hero  and  Grand  Isle. 

(Plattsburg  and  Rouses  Point  topographic  sheets.) 

General  remarks.  From  observations  made  in  the  season  of 
1920  on  the  island  which  includes  the  townships  of  South  Hero 
and  Grand  Isle,  suggestions  were  offered  as  to  how  the  relations 
among  the  formations  there  present  might  possibly  be  explained. 
These  suggestions  were  made  not  only  on  the  basis  of  conditions 
on  the  island,  but  also  in  the  light  of  careful  studies  of  the  field 
relations  at  other  places  in  the  lake  region,  particularly  in  Shore- 
ham  and  Orwell. 

While  camping  on  the  island  in  the  summer  of  1921,  parts  of 
it  which  had  not  been  personally  visited  before  were  inspected 
and  excursions  were  made  to  the  New  York  side  of  the  lake. 

Principal  geological  features  of  the  island.  The  geology  of 
the  island  has  been  described  in  detail  by  Professor  Perkins.^ 


'  Third  Report  of  the  State  Geologist,  1901-02,  pp.  102-17? 


150  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

The  formations  of  the  island  may  be  briefly  described  as 
follows : 

1.  Limestones,  mostly  gray  or  gray- weathering,  generally  in 
rather  thick  beds,  frequently  very  massive,  more  or  less  altered 
by  granulation  and,  perhaps,  somewhat  in  certain  cases  by  dy- 
namic agencies ;  but  generally  not  marked  by  clearly  visible  in- 
ternal deformation  due  to  shearing.  These  rocks  include  a  small 
portion  of  Brainerd  and  Seely's  "Beekmantown,"  which  is  more 
fully  developed  on  Providence  Island  just  to  the  south  of  Grand 
Isle  and  parts  at  least  of  the  same  authors'  divisions  A,  B,  and  C  of 
the  Chazy.  These  rocks  occur  in  somewhat  disconnected  masses, 
chiefly  in  the  central  and  southwestern  portions  of  the  island. 
The  Chazy  shows  much  variation  in  color  and  the  different  divi- 
sions are  recognizable  on  the  basis  of  fossils.  The  small  area 
of  Beekmantown  at  the  south  end  of  the  island  was  considered  by 
Seely  and  Perkins  to  belong  to  division  E  of  Brainerd  and  Seely's 
classification. 

2.  Other  limestones,  generally  in  contrast  with  those  of 
1  in  being  composed  of  prevailingly  much  thinner  beds,  but  in- 
cluding somewhat  massive  blackish  rocks  of  Black  River  age. 
All  belong  to  a  series  which  is  apparently  marked  at  the  base  by 
heavy  Black  River  beds  and  overlying  fairly  pure  limestones  of 
Trenton  age  and  which  ascends  through  a  sequence  of  mud  rocks, 
all  more  or  less  limy,  but  including  fairly  pure  limestone  beds. 
The  members  vary  in  color  from  gray  to  bluish-black,  the  latter 
usually  weathering  to  a  gray.  In  these  rocks  granulation  is  not  at 
all  marked.  The  sequence  from  base  to  top  is  interrupted  by  dis- 
placements so  that  it  is  not  as  well  shown  on  this  island  as  at  some 
other  places  in  the  lake  region  which  will  be  mentioned  beyond. 
The  alternations  from  one  kind  of  rock  to  another,  from  fairly 
pure  limestone  to  more  argillaceous  material,  suggest  oscillations 
of  level  and  other  conditions  which  operated  to  cause  changes  in 
the  character  of  the  deposits  from  time  to  time  and  changes  in 
the  character  of  the  fauna  as  well.  As  would  be  supposed,  there 
are  also  shown  lateral  gradations  or  variations  in  the  same  beds. 
Frequently  limestone  apparently  takes  the  form  of  small  lenses 
in  more  argillaceous  rocks.  All  the  conditions  indicate  that  dur- 
ing the  times  of  deposition  of  this  series,  muds  were  contending 
with  limestones,  over  which  they  finally  gained  ascendency.  Some 
portions  of  this  mud-limestone  series  are  barren  of  fossils.  In 
others  they  are  scarce.  There  is  an  interesting  recurrence  in 
low  horizons  within  the  shales  of  forms  marking  the  basal  beds 
which  have  a  typical  Trenton  fauna  ("Glens  Falls".) 

This  formation  of  limestones  and  irregularly  repeated  muddy 
limestones  and  limy  muds  passes  upward  into  the  rocks  described 
under  3. 

3.  Prevailingly  blackish,  shaly  mud  rocks,  still  often  if  not 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  151 

usually  limy,  effervescing  with  cold  dilute  acid,  but  characterized 
by  persistently  finer  grain.  In  their  bedded  features  they  are 
not,  however,  uniformly  thinly-bedded  shales.  The  beds  can  be 
seen  to  vary  in  thickness  from  a  fraction  of  an  inch  to  an  inch  or 
more  and  are  interbedded  with  siliceous  bands  of  tougher  texture 
which  break  with  subconchoidal  fracture  and  are  often  from  six 
to  eight  or  more  inches  thick.  These  various  shaly  rocks  have 
over  wide  areas  a  splintery  character  due  to  pronounced  shearing 
across  the  bedding,  giving  a  kind  of  slaty  structure. 

Contacts  of  the  members  given  under  1  with  those  of  2  and 
3  are  mostly  wanting  and  their  structural  relations  are,  therefore, 
more  or  less  problematical  and  open  to  such  interpretation  as  the 
general  structural  features  of  the  region  might  suggest.  The 
higher  members  of  2  probably  pass  upward  into  the  lower  beds  of 
3,  but  there  are  present  well-defined  displacements  which  actual 
contacts  do  not  seem  necessary  to  demonstrate. 

Attention  has  been  directed  by  different  observers  to  'the 
differences  shown  at  the  present  time  among  the  formations  of 
the  island  with  regard  to  the  extent  to  which  or  the  manner  in 
which  they  have  been  respectively  affected  by  dynamic  agencies. 

The  rocks  belonging  to  group  3,  as  defined  above,  perhaps 
make  up  the  larger  part  of  the  island.  They  are  generally  char- 
acterized by  pronounced  deformation.  Folding  and  tilting  are 
common;  but  even  in  places  where  neither  of  these  is  marked, 
they  are  when  only  slightly  buckled  or  lying  nearly  flat  distin- 
guished by  a  strongly  developed  cleavage.  But  this  shearing  struc- 
ture is  not  confined  to  the  members  of  group  3  alone ;  it  is  found 
in  much  of  fine  grained  limestone  of  category  2. 

This  shearing  structure  has  undoubtedly  led  to  confusion  in 
the  field  among  different  horizons  of  the  younger  members  of 
the  Ordovician  series.  In  surface  outcrops,  particularly  small 
ones  projecting  through  the  clay  or  drift,  all  that  may  be  visible 
is  an  irregular  erosion  surface  of  apparently  more  or  less  flatfish 
beds  which  have  been  sheared  into  slates  which  do  not  differ  much 
in  appearance,  whether  they  belong  to  group  2  or  group  3.  This 
circumstance  is  of  importance  because  without  appreciation  of 
it  the  real  character  of  a  rock  in  its  present  surface  exposure 
may  not  be  recognized. 

From  the  conditions  shown  on  Grand  Isle,  Perkins^  was  early 
led  to  regard  a  considerable  portion  of  the  limestones  with  inter- 
bedded muds  as  forming  a  transitional  series  between  the  Tren- 
ton and  the  "Utica."  The  probable  occurrence  of  such  a  "transi- 
tional series"  in  the  Champlain  basin  has  also  been  suggested  by 
other  observers.^  From  a  study  of  fossils  from  the  younger  lime- 
stones and  shales  of  the  Champlain  region,  Ruedemann^  came  to 

1  Perkins,  Third  Report,  1902,  The  Geology  of  Grand  Isle 

2  White,  Bull.  Geol.  Soc.  Amer.,  No.  10,  1899,  pp.  452-462. 

=  Ruedemann,  Twelfth  Report  Vt.  State  Geol.,  1920,  pp.  90-100 


152  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

the  conclusion  that  the  "Ordovician  series  ends  in  Vermont  with 
beds  no  younger  than  the  Trenton  group."  The  thinly-bedded 
limestones  of  the  basal  beds  are  true  Trenton  ("Glens  Falls  hori- 
zon"). The  black  mud  rocks  of  the  Champlain  basin  in  the 
south  (for  example,  around  Panton)  consist  entirely  of  Canajo- 
harie  shale  ;  in  the  north  they  are  "prevailingly  of  the  'Stony  Point' 
shale.  In  the  middle  they  meet,  the  'Stony  Point'  shale  resting 
upon  the  Canajoharie  shales  on  Grand  Isle  and  in  the  Vermont 
portion  of  the  northern  part  of  the  basin." 

Most  of  the  rather  barren  black  shale  in  the  northern  part 
of  the  basin,  carrying  Triarthnis  becki  and  Glossograptus  qiiadri- 
mucronatus  as  its  prominent  fossils,  which  extends  from  the 
Canadian  line  southward  over  the  islands  of  the  lake  and  along 
the  mainland  of  Vermont,  is  thought  by  Ruedemann  to  be  the 
equivalent  of  his  "Stony  Point"  shale  and  to  be  homotaxial  with 
late  Trenton  and,  therefore,  older  than  true  Utica.  Ulrich  con- 
curs with  Ruedemann  in  the  opinion  that  no  true  Utica  exists  in 
the  Champlain  basin. 

On  Grand  Isle  the  thinly-bedded  basal  Trenton  rocks  form  a 
ridge  about  a  mile  east  of  the  west  shore  of  the  island,  running 
from  a  point  southeast  of  Sawyer's  Bay,  where  they  are  in  prox- 
imity to  Chazy  beds,  northward  to  the  latitude  of  Gordon  Land- 
ing. At  numerous  places  they  yield  characteristic  basal  Trenton 
fossils.  For  the  most  part  these  beds  are  not  crushed  nor  sheared, 
although  at  some  places  they  have  buckled  and  sheared  somewhat, 
showing  clearly  that  they  have  experienced  lateral  pressure. 
Except  where  buckled  into  small  folds  these  rocks  appear  to  lie 
in  a  flattish  position,  dipping  gently  easterly.  They  do  not  ap- 
pear to  form  a  part  of  a  true  anticlinal  fold.  The  western  out- 
crop of  the  beds  forms  a  slope  of  variable  inclination  as  now 
eroded.  This  slope  east  of  Sawyer's  Bay  clearly  marks"  a  former 
shore  of  the  Champlain  water  body.  There  is  a  topographic 
breach  in  this  Trenton  ridge  northeast  of  Rockwell  Bay.  It  seems 
probable  that  these  rocks  formerly  had  an  extension  west  of  their 
present  western  margin. 

The  muddy  limestones  with  included  shaly  layers  which  occur 
along  shore  north  of  Rockwell  Bay  appear  to  be  younger  than  the 
beds  forming  the  ridge  just  described.  They  also  lie  in  flattish 
position,  but  take  on  a  slight  northerly  pitch  about  one-fourth  of 
a  mile  north  of  Rockwell  Bay.  These  rocks  have  strong  resem- 
blance to  beds  which  lie  above  the  basal  Trenton  near  Crane 
Point  in  Addison  County,  which  will  be  described  more  fully 
later.  Around  Gordon  Landing  the  rocks  are  of  more  muddy 
texture  than  are  those  southward  and  are  even  more  thickly- 
bedded.  Near  Gordon  Landing,  although  bedding  is  distinct,  the 
rocks  are  sheared  with  easterly  dipping  cleavage,  so  that  surface 
exposures  away  from  shore  have  the  appearance  of  slates. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  153 

A  little  way  north  of  Rockwell  Bay,  in  a  layer  near  the 
water,  Isoteliis  occurs  with  Prasopora,  paralleling  the  conditions 
near  Crane  Point  where  Prasopora,  which  sometimes  makes  up 
almost  an  entire  bed  in  the  basal  series,  as  it  does  also  on 
Grand  Isle,  recurs  occasionally  in  certain  layers  of  the  muddy 
rocks  which  lie  above  the  basal  series. 

Between  the  west  shore  of  the  island  at  Gordon  Landing 
and  the  slope  of  the  ridge  of  basal  beds  east  of  it  there  is  much 
surface  covering;  but  from  the  general  field  relations  and  the 
attitude  of  the  layers  along  shore  and  in  the  ridge  there  is  nothing 
that  suggests  an  anticlinal  fold  so  that  the  so-called  younger 
beds  along  shore  could  be  interpreted  as  lying  above  the  basal 
beds  on  the  western  limb  of  such  fold. 

North  of  Gordon  Landing  the  rocks  in  some  places  have 
resemblance  to  the  basal  Trenton  and  at  others  to  the  beds  north 
of  Rockwell  Bay.  At  the  Grand  Isle  landing  of  the  Cumberland 
Head  ferry  in  a  thick  layer  near  the  water-level  there  were  found 
specimens  of  Sinuites  cancellatus,  fragments  of  Calym-ene,  and 
small  orthocerata.  The  thick  layer  just  referred  to  is  succeeded 
northward  and  upward  by  an  imperfectly  alternating  series  of 
layers,  some  of  which  are  dark  colored  and  sheared,  while  others 
are  lighter  colored,  as  weathered  and  usually  non-sheared.  It  is 
somewhat  surprising  to  observe  these  rather  strongly  sheared 
layers  lying  between  others  which  show  no  marked  cleavage. 
Among  the  mud  rocks  this  condition  not  infrequently  occurs 
within  a  considerable  thickness  of  beds  which  do  not  show  any 
prominent  mass  deformation  and  which  often  lie  nearly  flat. 

Although  the  beds  near  the  ferry  landing  are  not  greatly 
deformed,  in  general  there  is  more  evidence  of  disturbance  from 
pressure  in  the  rocks  between  Gordon  Landing  and  Camp  Ver- 
mont than  in  the  shore  section  south  of  the  landing.  This  dis- 
turbance is  shown  in  the  form  of  minor  buckling  and  occasional 
ruptures,  as^^well  as  by  mashing  and  by  the  shearing  which  has 
been  mentioned. 

There  is  acceptable  suggestion  of  an  east-west  fault  at  Rock- 
well Bay,  the  "transition  beds"  lying  against  the  Chazy,  although 
the  contact  is  not  visible.  There  is  also  suggestion  of  a  break  at 
Gordon  Landing,  with  the  beds  at  the  north  occupying  the  up- 
throw side. 

The  ridge  that  has  been  described  above  as  composed  of 
the  basal  Trenton  beds  can  be  followed  only  a  short  distance 
north  of  the  latitude  of  Gordon  Landing.  Northward  over  areas 
that  have  been  mapped  as  "Utica"  the  surface  outcrops  are  few 
and  usually  not  clear  as  to  horizon.  In  some  places  the  rock 
might  without  much  hesitation  be  correlated  with  the  "transi- 
tional series"  of  limestones  and  shales  rather  than  with  the  higher 
black  shale  beds ;  but  extensive  shearing  and  absence  of  fossils 


154  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

make  it  difficult  to  decide  the  matter,  particularly  in  low  surface 
outcrops,  such  as  these  rocks  usually  present. 

From  Wilcox  Cove  northward  the  shore  section  displays  a 
series  of  beds  which  are  predominantly  shaly,  with  some  bands 
of  siliceous  rock,  the  whole  lying  nearly  flat.  While  there  is  some 
crushing  these  rocks  are  not  much  tilted. 

The  formation  of  black  shale  on  this  island,  and  in  most  of 
its  exposures  among  the  islands  to  the  north,  as  well  as  on  the 
mainland,  has  primary  structures  which  serve  to  distinguish  it 
from  the  more  limy  rocks  that  are  thought  to  be  transitional  from 
the  basal  Trenton  beds  into  it.  Even  when  strongly  sheared  the 
black  shale  formation  may  be  seen  to  comprise  members  of 
variable  thickness,  as  has  been  mentioned  above,  some  of  which 
are  distinctly  shaly,  while  others  are  of  firmer  character  and  more 
siliceous.  These  different  members  are  separated  by  distinct 
parting  planes  which  come  out  most  sharply  when  the  rocks  have 
been  folded  or  tilted.  But  the  more  shaly  or  muddy  beds  are 
marked  in  addition  by  fine  laminations  which  often  give  an  ap- 
pearance of  fine-grained  wood.  These  laminations  show  most 
clearly  when  the  rock  has  been  weathered,  the  weathering  process 
having  the  effect  of  emphasizing  the  slight  differences  in  the  com- 
position of  the  laminae.  One  is  tempted  to  speculate  on  the  con- 
ditions that  could  have  produced  these  laminations  which  have 
so  much  resemblance  to  seasonal  accumulations. 

The  "primary"  shaly  character  of  these  muds  is  due  to 
these  laminations,  but  there  is  often  shown  an  imperfect  separa- 
tion under  impact  which  may  be  an  expression  of  a  tendency  to 
minor  lenticular  segregation  of  the  more  limy  from  the  less  limy 
portions  of  mud  in  a  sea  in  which  limy  deposits  were  contending 
with  argillaceous  material,  but  in  which  there  was  always  more 
or  less  admixture  of  the  two.  Many  of  the  laminations  in  the 
beds  so  distinguished  are  of  rusty  brown  color,  in  which  they 
resemble  the  more  siliceous  bands  interbedded  with  the  shales. 

Over  the  eastern  part  of  the  island  the  rocks  which  have  been 
mapped  as  "Utica"  probably  include  some  beds  which  belong  to 
the  "transitional  series."     The  rocks  at  Allen  Point  may  be  such. 

North  of  South  Hero  station,  in  the  railway  cut  near  the 
overhead  bridge,  are  outcrops  of  rock  much  like  that  north  of 
Rockwell  Bay,  and  similar  rock  occurs  just  east  of  the  station 
along  the  main  highway.  The  beds  in  these  outcrops  have  not 
been  much  disturbed  from  the  horizontal  and  in  the  railway  cut 
on  both  sides  the  dip  may  be  plainly  observed  at  an  angle  of 
about  15  degrees  easterly.  The  rock  is  sheared,  giving  a  splintery 
structure. 

Again,  along  the  road  from  South  Hero  station  to  Sandbar 
Bridge,  a  mile  east  of  the  station,  some  of  the  low-lying  ledges 
seem  to  be  sheared  limy  rocks  like  those  of  the  cut  just  mentioned. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  155 

Towards  Sandbar  Bridge  the  rocks  are  blacker  and  more  shaly. 
It  would,  therefore,  seem  that  there  is  a  gradation  eastward  from 
the  basal  Trenton  through  a  "transitional  series"  to  blacker,  more 
shaly  rocks  hke  that  which  with  some  interruptions  may  be  traced 
along  the  west  shore  of  the  island  from  Rockwell  Bay  northward. 

Cedar  and  Fish  Bladder  Islands.  These  islands  were  visited 
with  a  suspicion  that  they  would  be  found  to  be  made  up  of  the 
shale  formation ;  but  as  they  would  serve  to  carry  the  inspection 
of  the  lake  rocks  eastward  towards  the  Vermont  mainland  it 
was  kept  in  mind  that  possibly  some  overthrust  rocks  might  be 
found.  There  was  seen  no  evidence  of  any  kind  to  indicate  that 
at  the  present  time  the  slates  of  these  islands  have  any  traces  of 
older  rocks  lying  on  them. 

On  these  small  islands  the  rocks  which  are  shales  are  exposed 
in  high  cliffs  around  their  shores,  but  are  concealed  by  clay  over 
their  central  portions.  Savage  Island  was  not  visited.  The 
Vermont  Report  shows  it  to  be  composed  of  the  shale. 

The  rocks  of  Cedar  and  Fish  Bladder  Islands  are  entirely 
similar,  and  are  laminated  muds  with  firmer  layers,  such  as  have 
been  described.  Recognizing  in  these  laminations  a  primary  char- 
acter it  is  clear  that  the  beds  of  these  islands  have  been  terribly 
jammed  and  mashed,  and  distorted  in  the  most  amazing  manner. 
The  deformation  is  largely  that  of  fracture;  once  continuous 
layers  have  been  broken  into  chunks  which  have  been  separated 
from  each  other  and  mashed  together,  producing  a  sort  of  brec- 
ciation.  Cleavage  is  also  pronounced.  At  some  places  it  appears 
that  small  blocks  have  moved  over  other  parts  of  the  formation, 
but  such  displacements  were  never  very  extended. 

Kibbie  Point.  At  Kibbie  Point  on  the  main  island  are  rocks 
similar  in  their  several  structural  features  to  those  south  of  Sand- 
bar Bridge  and  those  of  the  islands  just  described.  Distortion 
and  shearing  are  plainly  manifest.  At  this  place  a  minor  thrust 
was  noted  which  did  not  appear  to  pass  beyond  the  immediate 
exposure  involved. 

Robinson  Point.  At  Robinson  Point,  four  miles  north  of 
Kibbie  Point,  in  the  northeastern  part  of  the  island,  the  laminated 
shales  are  apparently  not  so  badly  mashed  as  in  the  southeastern 
part.  They  are  disposed  in  rather  gentle  folds  as  can  be  deter- 
mined from  the  laminations,  which  are  usually  the  only  means  of 
identifying  the  stratification.  The  bedding  is  very  often  obscured 
by  cleavage.  This  cuts  the  bedding  at  different  angles  as  a  con- 
sequence of  buckling  which  preceded  the  shearing.  At  Robinson 
Point  the  stratification  dip  is  about  15  degrees  westerly,  while  that 
of  the  cleavage  is  60  degrees  easterly.  Shearing  has  often  pro- 
duced a  rough  jointing  which  might  be  mistaken   for  bedding. 


156  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

It  is,  however,  uneven,  giving  a  ragged,  splintery  structure.  In 
many  places  bedding  and  cleavage  dip  in  the  same  direction, 
although  the  two  dips  do  not  coincide  in  most  cases. 

In  common  with  all  the  areas  in  the  lake  region  the  north- 
eastern part  of  this  island  shows  at  some  places  local  disturbances 
of  the  slate  by  folding  and  minor  crushing,  but  these  particular 
features  are  not  so  marked  in  present  exposures  in  this  part  of 
the  island  as  at  other  places. 

Occasionally  in  these  rocks  one  of  the  firmer  siliceous  beds 
will  be  seen  to  have  buckled  into  gentle,  wavy  folds,  while  the 
laminated  muds  above  and  below  show  no  apparent  folding,  but 
instead  a  more  or  less  prominent  cleavage  induced  by  the  same 
pressure  that  folded  the  firmer  band.  This  is  but  one  instance 
of  the  ease  with  which  the  shales  accommodated  themselves  to 
pressure  by  shearing. 

Calcite  veining  is  very  common  among  the  shales  in  the  east- 
ern part  of  this  island  and  sometimes  indicates  mashing  when 
such  is  not  very  apparent  from  any  other  structures. 

As  well  seen  in  clifif  exposures  the  way  a  mass  has  behaved 
under  shearing  stress,  even  when  bedding  structure  is  largely 
destroyed,  affords  a  means  of  telling  whether  the  rocks  were 
originally  shaly  or  somewhat  more  massive.  The  more  thinly- 
bedded  rocks  will  give  a  slaty  or  finely  splintered  rock,  while  the 
thicker  beds  will  be  coarsely  splintered,  or  sometimes  roughly 
jointed. 

A  rather  careful  inspection  of  Grand  Isle,  joined  with  an 
examination  of  the  rocks  of  North  Hero,  Alburgh  peninsula. 
Isle  La  Motte,  some  of  the  smaller  islands,  and  the  Vermont  main- 
land, shows  that  the  Ordovician  rocks  of  the  Champlain  basin, 
above  the  Beekmantown,  are  well  represented  on  Grand  Isle, 
and  that  some  of  the  shales  belong  in  the  higher  portions  of  the 
shale  formation.  On  Grand  Isle  fossils  from  these  higher  hori- 
zons are  rare,  probably  largely  because  of  shearing ;  but  in  litho- 
logical  characters  the  rocks  are  closely  comparable  to  and  seem 
susceptible  of  indentification  with  similar  rocks  in  the  upper  part 
of  the  shale  formation  in  many  of  the  other  parts  of  the  region 
as  named  above. 

The  shore  sections  of  the  islands  and  the  rocks  along  the 
mainland  from  the  Canada  line  to  the  southern  limit  of  the  lake 
show  that  the  various  submerged  channels,  passages  and  bays  that 
now  form  the  basin  known  as  Lake  Champlain  are  practically 
throughout  excavated  in  the  softer  rocks  belonging  to  the  transi- 
tional series  of  limestones  and  shales  or  to  the  higher  black  shales 
of  the  basin.  But  on  both  the  islands  and  the  mainland,  some- 
times forming  parts  of  the  present  lake  shore,  are  areas  of  older 
and  very  dift'erent  kind  of  rock  whose  relations  to  the  shales  form 
some  of  the  problems  of  the  region. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  157 

Structure  of  Grand  Isle.  Certain  apparently  possible  in- 
terpretations of  the  structural  relations  of  the  rocks  of  Grand 
Isle  were  discussed  in  the  writer's  first  paper  in  the  light  of  such 
studies  as  it  had  been  possible  to  make  up  to  the  time  of  its  publi- 
cation. Attention  was  directed  to  the  secondary  structural  dif- 
ferences shown  by  the  rocks  of  the  island.  It  was  pointed  out 
that  a  large  portion  of  the  formation  including  the  transitional 
series  and  overlying  black  shales  might  be  somewhat  sharply  dif- 
ferentiated from  the  massive  strata  of  Beekmantown  and  Chazy 
ages.  The  deformational  features  shown  by  much  of  the  transi- 
tional and  shale  series  were  noted  and  it  was  indicated  that  in  the 
crushed  condition  of  these  rocks,  now  manifested  by  minor  fold- 
ing and  tilting,  minor  reverse  faulting,  mashing  and  coarse  brec- 
ciation,  and  different  modes  of  shearing,  they  stand  in  contrast 
to  the  more  massive  strata  of  the  island.  The  Beekmantown  and 
Chazy  beds  were  shown  to  have  a  generally  flattish  position  in 
most  of  their  exposures,  particularly  in  the  western  half  of  the 
island,  and  not  to  be  notably  sheared,  although  somewhat  de- 
formed by  pressure  along  or  near  their  eastern  margins.  The 
Black  River  and  the  basal  Trenton  beds  making  up  the  ridge  that 
has  been  described  above,  were  also  shown  to  lie  rather  flat, 
although  the  latter  were  described  as  showing  minor  buckling 
and  shearing  at  some  places. 

Before  passing  to  the  discussion  of  the  possible  significance 
of  the  structural  differences  shown  by  these  Grand  Isle  rocks  as 
the  result  of  differences  in  behavior  under  dynamic  stresses  it 
may  be  worth  while  to  consider  other  differences  of  secondary 
character  which  some  of  them  show. 

The  Beekmantown  and  Chazy  rocks  give  an  impression  of 
having  suffered  certain  alterations  before  the  formation  of  the 
younger  beds.  The  features  referred  to  do  not  seem  to  represent 
on  a  minor  scale  or  to  be  in  the  same  class  with  those  which  in 
similar  rocks  of  the  region  have  more  or  less  clearly  been  due 
to  dynamic  pressure,  which  in  addition  to  producing  metamor- 
phism  by  crystallization  also  caused  flowage  and  cleavage  in  dif- 
ferent degrees,  with  the  formation  of  marble  or  marbly  rocks. 
The  particular  alterations  mentioned  appear  to  be  due  rather  to 
static  metamorphism  of  the  rocks.  As  has  been  mentioned,  they 
are  apparently  largely  of  the  nature  of  granulation  which  has 
more  or  less  completely  changed  the  original  material  and  pro- 
duced a  tough  rock  from  which  fossils  are  extracted  with  much 
difficulty.  In  some  parts  of  the  Champlain  region  rocks  which 
have  thus  been  altered  have  also  been  changed  further  by  dynamic 
metamorphism  and  in  such  cases,  of  course,  the  earlier  alteration 
features  are  blended  with  those  of  later  date  or  are  quite  concealed. 
Gradations  occur.  In  those  rocks  not  much  affected  by  dynamic 
agencies  the  fossils  retain  their  outlines  more  or  less  perfectly, 
although  crystallization  may  have  destroyed  details.  In  other  rocks 


158  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

the  features  resulting  from  static  metamorphism  are  very  evident, 
but  other  characters  resuUing  from  shearing  stress  appear  in  the 
shape  of  distortion  of  fossils  and  flowage  or  cleavage.  In  still 
other  rocks,,  pressure  has  more  completely  obscured  the  older  static 
features  with  the  destruction  or  almost  complete  obliteration  of 
fossil  remains. 

On  Grand  Isle  the  metamorphic  characters  of  the  Beekman- 
town  and  Chazy  rocks  appear  to  be  due  chiefly,  if  not  wholly,  to 
static  changes.  Absence  of  shearing,  lack  of  distortion  of  fossils, 
apparent  absence  of  mass  deformation  by  folding  and  other 
features  all  point  to  such  conclusion.  If  these  rocks  generally  had 
suffered  any  internal  deformation  they  should  give  more  evidence 
of  it,  comparable  with  such  as  is  found  in  other  and  similar  rocks 
of  the  region,  some  of  which  are  clearly  of  similar  age  while 
others  probably  are.  Such  deformation  as  these  rocks  may  have 
experienced  probably  involved  extensive  mass  dislocation,  rather 
than  what  might  be  called  internal  adjustment,  except  as  the 
latter  was  locally  developed  at  some  places. 

The  static  alteration  features  of  these  massive,  granular 
limestones  give  them  an  appearance  of  antiquity  in  contrast  with 
the  rocks  with  which  they  are  associated.  In  the  Black  River  and 
basal  Trenton  beds  there  is  not  present  apparently  the  same  de- 
gree of  alteration  by  granulation  as  the  Beekmantown  and  Chazy 
beds  show.  In  these  differences  there  is  offered  an  indication 
quite  distinct  from  that  which  fossils  show  of  a  hiatus  between 
the  Canadian  and  Mohawkian  of  the  Champlain  region.  One  is 
tempted  somewhat  to  speculate  on  what  the  conditions  were  which 
led  to  the  induration  of  the  older  rocks. 

As  was  discussed  in  the  first  paper  it  has  usually  been  as- 
sumed that  there  has  been  no  great  amount  of  lateral  disturbance 
of  any  of  the  formations  now  found  on  Grand  Isle,  that  the 
various  rocks,  including  the  masive  limestones  of  the  Beekman- 
town and  Chazy  formations,  rest  now  substantially  where  they 
were  formed.  Unfortunately,  the  conditions  on  the  island  at  the 
present  time  do  not  allow  of  positive  determination  of  the  relations 
between  the  massive  limestones  and  the  younger  rocks.  It  was 
not  possible  to  find  any  contacts  of  the  former  on  the  latter  any- 
where on  the  island.  The  idea  that  there  has  been  displacement 
of  the  rocks  of  the  island  rests  upon  the  considerations  that  such 
kind  of  deformation  is  widely  prevalent  in  and  characteristic  of 
the  region  and  that  the  rocks  of  the  island  show  the  effects  of 
profound  pressure. 

It  was  first  supposed  that  the  shale  formation  of  the  whole 
region  had  undergone  more  severe  folding  as  a  whole,  than 
now  appears  to  have  been  the  case,  even  in  the  eastern  portion  of 
the  basin  where  the  pressures  might  reasonably  be  assumed  to 
have  been  more  powerful.     The  comparatively  small  number  of 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  159 

exposures  which  it  had  been  possible  to  inspect  when  such  a  view 
was  formulated  seemed  to  indicate  that  the  shales  were  usually 
disposed  in  rather  large  close  folds  with  o^^erturning  and  conse- 
quent isoclinal  structure.  For  places  where  the  shales  had  clearly 
been  overridden  by  older  rocks  along  thrust  planes  they  were 
discussed  and  pictured  as  having  a  prevaiHngly  easterly  dip,  which 
was  attributed  to  overturning.  The  conditions  noted  in  a  more 
extensive  study  of  the  region  and  from  an  examination  of  the 
shale  formation  in  widely  separated  localities  contradict  such  a 
view  and  have  afforded  data  for  a  revision  of  ideas. 

Any  severe  buckling  or  folding  which  the  shales  show  now 
seem  to  be  more  or  less  local  corrugations  which  pass  along  the 
strike  into  crush  zones  or  fault  fractures,  or  perhaps  eventually 
into  relatively  gentle  flexures  marked  only  by  a  profound  cleavage. 
Across  the  strike  also  these  localized  zones  of  severe  folding, 
fracturing  and  mashing  will  apparently  pass  into  gently  undulating 
folds.  Eastward  toward  the  areas  of  the  region  marked  by  over- 
thrust  of  older  rocks  on  the  shales  the  latter  are  more  generally 
crushed  and  tilted,  but  at  some  places  not  far  from  the  present 
margin  of  overthrust  rocks  they  are  notably  flat,  as  indicated  by 
bedding  and  laminations,  although  when  flat  they  are  always 
strongly  sheared  with  the  development  of  fracture  cleavage. 

What  then  are  some  of  the  conclusions  to  be  drawn  from 
the  flat  position  or,  generally  speaking,  open  folds  which  these 
different  rocks  show,  perhaps  having  Grand  Isle  principally  in 
mind  at  this  point?  These  rocks  have  clearly  been  acted  upon 
by  powerful  compressive  forces.  This  is  shown  on  Grand  Isle, 
but  more  clearly  at  other  places.  In  the  absence  of  any  folding 
of  large  dimensions,  or  even  universal  close  folding  of  small 
dimensions,  the  inference  is  strong  that  these  rocks  yielded  to 
pressure  chiefly  through  shearing  of  one  kind  or  other.  In  this 
particular  the  massive  limestones  behaved  like  the  shales ;  but 
in  the  former  the  shearing  did  not  always  manifest  itself  as  an 
internal  deformation  with  the  development  of  fracture  cleavage 
or  other  pronounced  internal  structure  attributable  to  pressure, 
even  when  the  associated  shales  often  developed  such  structures 
to  a  high  degree.  On  Grand  Isle  the  massive  strata  have  clearly 
effectively  resisted  any  appreciable  internal  deformation  for  the 
most  part.  If  this  is  not  the  correct  interpretation  it  is  not  only 
difflcult  to  understand  their  own  characters  but  also  why  the 
much  less  massive,  thinly-bedded,  basal  Trenton  beds  in  west 
part  of  the  island  have  not  been  more  severely  deformed  in  all 
ways.  The  massive  beds  have  acted  as  a  buffer  for  the  younger 
rocks. 

What  then  has  probably  been  the  behavior  of  the  massive 
strata  under  pressure  if  they  have  not  buckled  or  sheared  with 
any  visible  flow  or  fracture  structures?  They  are  probably  to 
be  thought  of  as  having  moved  as  a  great  block  or  as  blocks  frag- 


160  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

mented  from  the  main  mass  with  which  they  were  once  joined. 
They  have  resisted  internal  deformation  in  some  places,  as  on 
Grand  Isle,  without,  however,  being  able  to  prevail  completely 
against  the  pressure.  They  were  competent  against  such  deforma- 
tion as  the  shales  exhibit,  but  not  resistant  enough  to  remain  in 
place.  From  a  consideration  of  the  very  different  primary  char- 
acters of  the  heavy  limestones  and  the  shales  it  is  not  difficult 
to  see  how  forces  competent  to  crush  the  shales  might  leave  the 
massive  limestones  practically  free  of  such  features,  but  since  it 
is  apparent  that  the  shales  could  hardly  have  been  so  generally 
crushed  or  sheared  without  diminishing  their  original  breadth 
from  east  to  west  to  a  marked  extent,  it  naturally  becomes  a  ques- 
tion of  how  the  massive  rocks  accommodated  themselves  to  the 
simultaneous  action  of  the  same  forces.  That  accommodation 
was  reached  in  some  places  in  the  lake  region  by  shearing  even 
in  the  massive  limestones  is  shown  in  numerous  cases,  but  on 
Grand  Isle  it  was  effected  chiefly  by  mass  dislocation. 

In  the  writer's  first  discussion  of  the  probable  structure  of 
Grand  Isle  (see  first  paper)  some  of  the  considerations  developed 
above  were  dwelt  upon,  but  a  good  deal  of  stress  was  put  upon 
present  conditions  among  similar  rocks  in  other  parts  of  the 
Champlain  region,  particularly  along  the  lake  shore  farther  south. 
In  Shoreham  and  Orwell  the  present  field  relations  leave  no  doubt 
that  older  formations  have  ridden  over  the  shales  along  thrust 
planes,  and  while  at  many  places  the  massive  beds  have  been 
somewhat  folded  and  fractured  and  sometimes  internally  de- 
formed, there  are  other  places  where  the  massive  beds  lie  nearly 
flat  with  little  evidence  of  internal  changes  resulting  from  pres- 
sure, although  the  rocks  may  be  altered  by  other  processes  as  is 
the  case  on  Grand  Isle.  The  so-called  "Potsdam"  and  "Beekman- 
town"  at  Mt.  Independence  in  Orwell  and  at  Mutton  Hill  in  Shore- 
ham  are  cases  in  point.  The  conditions  in  other  parts  of  the 
Champlain  basin  also  give  support  of  very  positive  character  to 
the  conclusion  that  massive  Lower  Ordovician  beds  similar  to 
those  on  Grand  Isle  have  been  moved  by  thrusts  and  are  not  now 
in  their  original  places. 

In  some  studies  which  the  writer  made  in  the  Hudson  valley 
region  near  Poughkeepsie,  New  York,  among  rocks  which  in  spite 
of  their  apparent  remoteness  from  the  Champlain  basin  have 
much  resemblance  to  certain  strata  of  the  basin,  not  only  in  re- 
spect to  age  and  general  lithology,  but  in  character  of  deforma- 
tion as  well,  there  seemed  to  be  acceptable  evidence  for  the  con- 
clusion that  massive  limestones  of  Lower  Ordovician  age  had 
been  thrust  through  younger  shales  by  reverse  faulting,  often 
with  a  horizontal  component  powerful  enough  to  drive  the  mas- 
sive rocks  in  a  lateral  direction  over  the  younger  beds  for  a  con- 
siderable but  usually  indeterminable  distance. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  161 

While  reverse  faulting  was  recognized  as  probably  playing  a 
part  in  the  disturbance  of  the  rocks  of  Grand  Isle,  so  that  they 
are  probably  to  be  regarded  as  crowded  somewhat  by  blocks 
riding  against  other  blocks,  the  view  was  rather  favored  (see  first 
paper)  that  the  Beekmantown  and  Chazy  beds,  and  some  of  the 
younger  rocks  as  well,  had  been  moved  along  a  "major"  thrust 
plane  that  had  sheared  beneath  them  after  they  had  been  broken 
by  earlier  reverse  faulting  and  had  transported  them,  perhaps 
for  a  long  distance,  from  the  east.  They  were  thought  of  as 
having  ridden  over  the  shales  that  form  the  eastern  part  of  the 
island,  as  well  as  others  which  intervene  between  the  island  and 
the  Vermont  mainland.  Largely  on  account  of  normal  faulting 
that  probably  occurred  subsequent  to  the  action  of  pressure  on 
these  rocks  it  is  not  now  possible  to  decide  whether  this  view  is 
correct,  or  whether  the  massive  rocks  have  simply  broken  through 
the  younger  beds  and  perhaps  have  travelled  only  a  short  distance 
over  the  shales  which  are  now  concealed  beneath  them.  '  In  this 
connection  it  should  perhaps  be  remembered  that  we  are  dealing 
with  an  eroded  and  a  sunken  region. 

From  relations  which  are  present  in  the  Taconic  hills  of  Sud- 
bury and  Orwell  it  was  conjectured  that  a  major  thrust,  like  that 
referred  to  above,  might  have  cut  in  such  way  as  to  carry  early 
Cambrian  strata  at  one  place  and  early  Ordovician  at  another  over 
the  shale  formation.  The  conjecture  rested  in  part  on  the  as- 
sumption that  early  Ordovician  beds  lay  unconformably  upon 
eroded  Cambrian  rocks.  The  conditions  in  the  Taconic  hills  are 
very  puzzling  and  require  further  detailed  study  with  reference 
to  this  point,  but  there  remains  little  doubt  of  the  existence  of 
thrusting  in  the  Taconic  range.  In  the  range  the  difficulty  is 
to  account  definitely  for  the  remarkable  present  distribution  and 
contiguity  of  what  appear  to  be  Lower  Cambrian  terrigenous 
rocks  and  certain  limestones  including  probably  lower  and  middle 
Ordovician  rocks. 

The  absence  of  large  folds  in  the  various  rocks  of  the  Cham- 
plain  basin  does  not  seem  to  fall  in  with  a  view  that  these 
formations  were  at  any  time  elevated  into  mountain  masses  by 
huge  and  extensive  plications  of  the  crust.  But  the  absence  of 
large  folds  does  not  militate  against  an  idea  that  there  may  well 
have  been  a  considerable  elevation  of  the  rocks  at  some  time  in 
their  history.  That  much  elevation  was  possible  seems  to  follow 
from  consideration  of  the  result  of  integrating  a  large  number 
of  thrusts  of  all  dimensions,  including  those  which  now  find  ex- 
pression in  cleavage.  The  statement  that  there  has  not  been  ex- 
tensive folding  on  a  large  scale  is  in  accord  with  facts  observed 
in  the  field.  Lack  of  such  folds  in  the  shales  seems  to  have  been 
the  direct  result  of  failure  to  fold  on  the  part  of  the  massive  beds 
which  underlay  them.  But  if  the  latter  were  thrust  into  the  shales 
in  varying  degrees,  sometimes  into  them,  sometimes  through  them 


162  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

and  sometimes  even  over  them,  the  effect  apparently  would  have 
been  to  produce  the  crushed  characters  which  they  now  show  and 
to  give  a  prominent  fracture  cleavage,  whether  the  shales  re- 
mained practically  flat  or  were  previously  buckled  into  small  folds 
or  jammed  into  crush  zones.  The  massive  rocks  are  in  the  posi- 
tion of  overthrust  with  reference  to  the  shales  that  lie  on  one  side 
of  them,  and  of  underthrust  with  respect  to  shales  that  lie  on 
the  other  side  and  above  them.  Either  relation  seems  sufficient 
to  account  for  crushing  and  shearing  of  the  shales. 

On  Grand  Isle  then  different  masses  of  rocks  are  probably 
to  be  thought  of  as  now  in  more  or  less  displaced  relations  with 
respect  to  one  another  as  the  result  of  compression.  But  the 
evidence  on  Grand  Isle  itself  is  inconclusive.  Features  elsewhere 
in  the  region  that  show  what  the  actual  behavior  has  been  and 
what  the  tendency  obviously  was  must  be  invoked  and  the  prob- 
able presence  of  a  common  plan  of  structure  for  the  region  must 
be  recognized  in  explaining  the  structure  of  Grand  Isle. 

It  may  as  well  be  stated  at  this  place  as  elsewhere  that  so 
far  as  observations  have  gone  on  the  Vermont  side  of  Lake  Cham- 
plain,  there  is  no  evidence  to  show  a  thrust  plane  cutting  beneath 
all  the  rocks  now  exposed  in  the  Champlain  basin.  If  such  plane 
exists,  perhaps  evidence  for  it  would  hardly  be  sought  on  the 
Vermont  side.  There  may  be  such  a  plane  cutting  at  c6nsiderable 
but  unknown  depth  and  having  its  line  of  emergence  in  older 
rocks  on  the  New  York  side  of  the  lake.  On  the  Vermont  side 
the  thrusts  of  various  magnitudes  which  cut  the  rocks  along  the 
general  strike  and  which  are  repeated  across  it  may  be  the  surface 
expression  of  a  deep-seated  shear,  but  the  major  thrusts  on  the 
Vermont  side  cut  above  the  weak  shales  of  the  region,  and  are 
themselves  apparently  modified  by  antecedent  faults  and  thrusts 
of  minor  dimensions. 

North  Hero  Township, 

(Rouses  Point  topographic  sheet.) 

The  township  of  North  Hero  comprises  several  small  islands 
of  varying  dimensions  and  two  larger  ones  which  are  joined  by 
a  narrow  neck,  a  portion  of  which,  known  as  the  "carrying  place." 
is  flooded  at  high  water.  These  various  insular  areas  are  all  of 
low  relief  and  are  made  up  of  the  shale  formation.  As  in  the 
case  of  Grand  Isle  the  most  satisfactory  exposures  are  found 
along  shore. 

While  there  are  some  minor  variations  in  the  bedded  char- 
acters of  the  rocks  of  the  North  Hero'  islands  they  are  prevail- 
ingly black,  limy  shales  with  occasional  firmer  bands  and  much 
like  those  of  the  northern  end  of  Grand  Isle,  showing  beds  of 
different  thicknesses  with  the  more  muddy  ones  distinctly  marked 
by  laminations,  accentuated  by  weathering,  vvliici*  appear  in  rock? 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  163 

that  have  been  strongly  sheared,  as  well  as  in  those  which  have 
not.  The  firmer  beds  are  composed  of  tougher,  more  siliceous 
material  than  the  associated  muds.  On  these  low  islands  with 
visibly  limited  vertical  range  of  beds  the  firmer  usually  rusty  beds 
do  not  so  frequently  appear  and  are  not  such  conspicuous  members 
as  on  the  Vermont  mainland,  where  they  serve  as  useful  features 
for  correlation.  On  North  Hero,  as  elsewhere,  these  rocks  are 
of  monotonous  aspect,  although  with  respect  to  the  degree  in 
which  they  are  now  sheared  and  cut  by  cleavage  they  show  con- 
spicuous differences  among  their  outcrops. 

The  rocks  were  examined  primarily  for  their  secondary  struc- 
tural characters.  In  their  primary  lithological  features  they  form 
a  fairly  homogeneous  mass  of  deposits  of  apparently  uninter- 
rupted sequence. 

Professor  Perkins  in  his  description  of  these  islands  has 
given  an  accurate  account  of  the  distribution  and  other  general 
characters  which  it  is  hardly  necessary  to  repeat,  except  as  it  may 
be  desirable  to  emphasize  certain  aspects  that  belong  to  a  discus- 
sion of  the  geology  of  the  whole  region. 

The  prominently  argillaceous  nature  of  the  shale  formation 
comes  out  strongly  from  the  manner  in  which  its  surface  portions 
have  weathered.  In  many  places  the  shale  may  be  seen  to  grade 
upward  into  clay  which  retains  the  primary  laminated  character 
of  the  original  rock.  While  the  surface  material  of  the  islands 
is  apparently  to  a  considerable  extent  of  glacial  origin,  much  of 
the  clay  is  purely  residual  material  which  has  probably  been 
largely  formed  since  the  glaciation  of  the  region.  Such  material 
is  apparently  nowhere  very  thick. 

While  the  shales  have  clearly  buckled  locally  under  pressure 
and  almost  always  show  cleavage  well  developed,  they  are  ap- 
parently more  commonly  disposed  in  gentle  swells  of  moderate 
lateral  extent  and  comparatively  small  vertical  displacement  so 
that  the  bedding  has  low  easterly  or  westerly  dip  and  the  axes  of 
the  folds  lie  horizontally  or  more  often  have  slight  northerly  or 
southerly  pitch.  Such  features  are  of  interest  with  respect  to  the 
deformational  history  of  the  region,  particularly  with  reference  to 
the  question  of  the  extent  of  the  region  involved  in  the  folding 
which  is  supposed  to  have  occurred  at  the  close  of  Ordovician 
time. 

Studies  made  on  North  Hero  seemed  to  show  that  the  shales 
are  more  severely  jammed  along  certain  north-south  belts  than 
along  others  and  that  even  shearing  as  expressed  by  fracture 
cleavage  shows  similar  geographical  segregation  and  is  more 
marked  in  some  places  than  at  others  even  on  the  same  meridians. 
Fossils  are  not  uncommon  in  parts  least  sheared,  so  far  as  fossils 
are  apparently  present  in  these  rocks  ;  but  where  shearing  has 
been  severe,  as  might  be  expected,  fossils  are  hard  to  find. 


164  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Some  of  the  outcrops  of  the  shore  sections  may  now  be 
briefly  described. 

On  the  island  that  Hes  just  north  of  Grand  Isle  the  rocks 
along  shore  between  Grand  Isle  bridge  and  City  Bay  lie  generally 
in  a  flattish  position,  from  the  bridge  northward  for  a  distance  of 
about  two  miles,  pitching  gently  to  the  north  and  then  changing 
to  an  equally  gentle  southerly  pitch.  Whether  the  rock  through- 
out the  distance  mentioned  all  belongs  to  the  eastern  limb  of  a 
common  anticlinal  fold  is  not  certain.  The  dip  is  predominantly 
easterly,  but  where  the  pitch  changes  to  southerly,  about  a  mile 
south  of  City  Bay,  the  rocks  appear  to  be  more  broken  by  rough 
compression  "joints"  and  shearing  planes  than  farther  south.  At 
several  places  graptolites,  probably  G.  quadrimucronatus,  and 
heads  of  T.  becki  were  found. 

Along  the  west  shore  of  this  island  similar  variations  in  direc- 
tion of  pitch  were  noted ;  at  Hazen  Point  the  shales  pitch  south- 
erly, less  than  a  mile  to  the  north  they  pitch  in  the  opposite  direc- 
tion. In  traversing  the  west  shore  one  walks  diagonally  over 
small,  gentle  anticlinal  and  synclinal  folds.  At  Hazen  Point  the 
dip  is  westerly,  a  mile  north  and  nearly  on  the  same  meridian  the 
dip  is  easterly.  Farther  north,  about  midway  of  the  shore,  the  dip 
changes  to  westerly.  Cleavage  is  usually  well  developed  along  the 
west  shore.  It  did  not  appear  that  one  type  of  fold  was  more 
marked  in  this  regard  than  the  other.  In  some  places  the  folds  are 
quite  symmetrical,  but  in  others  they  are  less  so  and  sharper  and 
the  beds  are  tilted  to  a  high  angle  or  even  to  a  vertical  position, 
and  are  sometimes  overturned.  Mashing  and  fracturing  of  beds 
are  common  in  the  sharper  folds  and  most  of  the  anticlinal  buckles 
show  some  modification  from  crushing.  Usually  these  crush  zones 
are  further  marked  by  veinlets  and  streaks  of  calcite.  Differences 
with  respect  to  the  expression  of  shearing  may  be  correlated 
definitely  with  primary  differences  in  the  characters  of  the  beds. 
In  both  easterly  and  westerly  dipping  beds  a  sort  of  jointing 
practically  perpendicular  to  the  bedding  and  parallel  or  diagonal 
with  the  strike  was  occasionally  noted,  especially  along  the  shore 
of  Pelot  Point  peninsula.  This  type  of  fracture  is  probably  also 
an  expression  of  shearing  strain.  Plates  XIX  and  XX  serve  to 
convey  ideas  of  the  nature  of  some  of  the  structures  more  clearly 
than  verbal  descriptions  could.  It  seems  as  though  folding  and 
fracture  sometimes  preceded  the  formation  of  cleavage,  as  though 
the  latter  were  the  final  expression  in  such  cases  of  the  shearing 
stress.  Probably,  however,  these  respective  deformations  were 
sequential  in  the  same  episode. 

If  it  were  assumed  that  there  was  considerable  lateral  varia- 
tion in  the  characters  of  the  beds  of  this  shale  formation,  it  is 
not  difficult  to  understand  that  at  some  places  along  the  same  gen- 
eral meridian  the  rocks  were  mashed  or  broken  by  faults  of  small 
displacement  and  that  at  others  sufficient  relief  came  from  frac- 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  165 

ture  cleavage  or  compression  jointing.  These  different  types  of 
deformation  clearly  belong  to  the  same  class  or  category  and, 
probably,  to  the  same  general  episode  of  disturbance. 

Along  the  west  shore  of  the  island  in  many  places  where  the 
rocks  were  not  too  badly  sheared,  graptolites  and  glabellas  of 
Triarthrus  hecki  were  found.  They  were  seen  most  abundantly 
just  north  of  Hazen  Point  and  along  the  shore  of  Pelot  Point 
peninsula.  Exceptionally  low  water  in  the  season  of  1921  allowed 
an  inspection  of  practically  the  entire  west  shore  section.  South 
of  Pelot  Point  the  shales  form  bold  cliffs  which  on  foot  are  im- 
passable except  at  low  water.  Possibly  the  rocks  contain  other 
fossils,  but  such  were  not  seen. 

The  shale  formation  continues  from  the  island  just  described 
to  the  one  just  north  of  it ;  but  on  this  northern  island  much  of 
the  shore  is  very  low  and  bowlder  strewn,  with  no  outcrops  of  the 
shale  now  visible.  Good  outcrops  occur  along  the  east  shore  in 
the  southern  part  and  on  the  west  shore  north  of  Blockhouse 
Point.  These  sections  show  the  same  kinds  of  rocks  and  fossils 
and  the  same  structures  as  those  found  on  the  island  just  south. 

Alburgh  Peninsula. 

(Rouses  Point  topographic  sheet.) 

The  topographic  and  geologic  features  of  Alburgh  are  quite 
like  those  of  the  North  Hero  islands.  The  peninsula  is  everywhere 
of  low  relief,  only  in  two  or  three  small  areas  rising  above  200  feet. 
Several  swampy  tracts  occur  and  some  of  these  probably  mark 
nearly  or  quite  complete  separation  of  the  hard  rock  formation  at 
the  present  water-level,  so  that  if  the  surface  material  which  now 
fills  them  were  removed  the  peninsula  would  be  resolved  into 
insular  or  smaller  peninsular  fragments  of  the  shale  formation. 

The  rocks  of  Alburgh  were  examined  over  the  interior  of 
the  peninsula  at  many  places  and  for  long  distances  where  exposed 
along  shore,  but  on  the  shore  and  inland  there  are  many  stretches 
and  areas  where  the  shales  are  not  exposed. 

Along  the  east  shore  bordering  Alburgh  Passage  there  is 
an  almost  continuous  outcrop  of  the  shale.  At  many  places  be- 
tween Wagner  Point  and  Point  of  the  Tongue  the  shales  dip 
easterly  at  low  angle  with  easterly  dipping  cleavage.  On  the 
west  shore  of  the  Point  of  the  Tongue  the  rocks  are  much  dis- 
turbed, like  those  on  the  west  shore  of  Pelot  Point  farther  south 
on  North  Hero.  Near  the  point  the  rocks  are  folded  into  a  fairly 
sharp  anticline.  Northward  the  beds  of  the  western  limb  stand 
at  a  high  angle  of  dip  and  still  farther  north  are  overturned  with 
high  easterly  dip,  with  shearing  in  the  direction  of  the  bedding. 

After  a  stretch  of  sandy  beach  the  rocks  outcrop  again  at 
Coon  Point,  whence,  with  a  slight  interruption  at  Palmer  Cove, 
they  continue  practically  without  break  along  the  shore  of  Isle 


1C6  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

La  Motte  Passage,  to  within  two-thirds  of  a  mile  of  the  toll 
bridge. 

At  the  western  end  of  "Sand  Beach,"  at  Coon  Point,  the 
shales  form  a  gentle  open  syncline.  This  is  followed  westward 
by  a  smaller,  unsymmetrical  anticlinal  fold  and  this  by  a  small, 
irregular  synclinal  flexure,  which  is  succeeded  by  a  broader  anti- 
clinal swell  and  this  in  turn  by  a  broken  syncline  whose  western 
limb  is  crushed  against  an  anticlinal  buckle.  All  the  deformational 
features  appear  to  have  been  the  result  of  compression.  Some 
portions  of  the  rock  had  apparently  become  wedged  between 
others  and  'confined,  so  that  under  continued  compression  there 
occurred  some  differential  movement  and  offsetting  giving  a 
structure  simulating  step  faulting  as  produced  by  gravitational 
tensional  stress.  The  beds  are  not  distinguished  by  strong 
cleavage. 

At  Coon  Point,  in  fact,  the  rocks  for  the  most  part  do  not 
show  pronounced  shearing  and  the  locality  is  an  excellent  col- 
lecting ground  for  fossils,  particularly  fragments  of  the  trilobite, 
Triarthrns  becki,  which  were  seen  here  in  abundance.  Graptolites 
were  also  found. 

In  the  section  along  the  west  shore  north  of  Coon  Point 
there  are  no  especially  noteworthy  structures  different  from  those 
which  have  been  described.  About  two  miles  north  of  the  point 
the  rocks  show  prevailingly  low  westerly  dip  and  carry  fossils 
like  those  at  Coon  Point;  a  series  of  vertical  joints  with  strike 
N.  about  52  degrees  east  cuts  the  shales  at  this  place. 

Just  north  of  the  Alburgh  end  of  the  Isle  La  Motte  toll 
bridge  is  a  high  cliff  in  the  shales  and  the  shore  road  cuts  through 
these  rocks.  At  this  place  the  rocks  are  severely  jammed  and 
the  laminated  beds  much  distorted  and  broken,  showing  great  dis- 
order. The  rocks  are  filled  with  veins  and  bunches  of  calcite. 
North  of  these  outcrops  the  shore  is  low  and  bowlder  strewn  with 
few  outcrops  as  far  as  Windmill  Point.  Between  Windmill 
Point  and  Rouses  Point  ferry  landing  the  shales  carry  graptolites 
and  fragments  of  trilobites  and  dip  westerly  at  a  low  angle  with- 
out conspicuous  cleavage. 

Ruedemann^  reports  a  list  of  fossils  from  alternating  black, 
calcareous  shales  and  black  to  dark  gray  impure  limestone  out- 
cropping along  the  lake  shore  one  and  a  half  miles  east  of  Wind- 
mill Point  which  leaves  "no  doubt  of  the  Trenton  age"  of  the 
beds. 


1  Twelfth  Report  of  Vt.   State.  Geol.,  p.   97. 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  167 

Along  the  road  that  crosses  the  peninsula  one  and  a  half 
miles  north  of  Isle  La  Motte  station  and  again  along  the  shore 
road  and  the  shore  near  Dillenbeck  Bay  the  shales  yielded  only 
graptolites  and  T.  becki.  The  same  fossils  were  found  at  East 
Alburgh  and  at  Alburgh  Springs  along  shore  and  also  in  some 
outcrops  along  the  road  between  Alburgh  Springs  and  Alburgh, 
west  of  Mud  Creek. 

The  prevailing  rocks  now  exposed  over  the  Alburgh  penin- 
sula are  the  black,  laminated  shales  and  the  conspicuous  fossils 
are  graptolites,  probably  G.  quadrimucronatus  and  fragments  of 
Triarthrus  becki. 


Isle  La  Motte. 

(Rouses  Point  topographic  sheet.) 

In  its  main  topographic  outlines  Isle  La  Motte  bears  much 
resemblance  to  Grand  Isle,  of  which  it  is  also  to  a  large  extent 
the  geologic  counterpart.  In  its  general  low  relief  it  is  like  the 
other  islands  of  the  lake  and  portions  of  the  Vermont  main- 
land. Its  rocks  were  noted  very  early  in  the  history  of  geological 
exploration  of  the  lake  region  and  have  been  more  recently  de- 
scribed and  mapped  by  Brainerd  and  Seely  and  by  Perkins.  In 
the  published  descriptions  of  the  rocks  their  outstanding  deforma- 
tional  characters  have  been  mentioned,  but  no  definite  attempt  has 
been  made  to  account  for  the  secondary  relations  which  the 
formations  have  to  one  another,  nor  to  correlate  the  conditions 
found  on  the  island  with  those  found  in  other  parts  of  the  region. 

Several  days  were  spent  in  a  careful  inspection  of  the  island 
and  the  following  brief  review  of  the  formations,  as  well  as  the 
more  particular  account  and  discussion  of  the  secondary  features 
are  based  upon  personal  acquaintance  with  the  rocks. 

The  formations  on  Isle  La  Motte  include  a  small  area  of  the 
uppermost  part  of  Brainerd  and  Seely's  Beekmantown,  exposed 
chiefly  along  shore  in  the  southern  part  of  the  island,  a  large  area 
of  Chazy,  including  parts  at  least  of  all  three  divisions  as  defined 
by  Brainerd  and  Seely  and  having  a  combined  thickness  as  meas- 
ured by  these  observers  of  about  500  feet^  a  small  patch  of  Black 
River  of  roughly  determined  stratigraphic  boundaries,  a  con- 
siderable area  of  Trenton  limestone,  and  three  relatively  small 
exposures  of  the  so-called  "Utica"  shale.  In  some  of  their  struc- 
tural characters  and  in  their  geographic  arrangement  many  of 
the  rocks  have  strong  resemblance  to  similar  rocks  on  Grand  Isle. 

The  Beekmantown  of  the  main  island  (Cloak  Island  will  be 
described  beyond)  is  confined  to  the  southern  end  known  as  "The 
Head."  Its  surface  extent  is  relatively  small,  although  its  shore 
section  is  nearly  a  mile  long.     The  top  of  the   formation  was 


168  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

drawn  by  Seely  and  Perkins  at  a  dark,  compact  layer  about  30 
inches  thick  which  carries  Isochilina  and  which  is  further  char- 
acterized by  breaking  into  large  cubical  blocks.  The  rest  of  the 
formation,  as  exposed  to  the  limit  of  low  water,  consists  of  firm 
and  shaly  beds,  varying  in  thickness  from  6  to  30  inches.  The 
rocks  pitch  in  a  general  northerly  direction  at  a  low  angle  of 
about  5  degrees  and  are  overlain  by  the  lower  Chazy.  The  gen- 
erally flattish  position  of  the  Beekmantown  beds  and  their  lack 
of  any  shearing  deformation  are  noteworthy  features.  Their 
primary  characters  have  been  sufficiently  described  by  other 
observers. 

The  Chazy  strata,  which  succeed  the  Beekmantown,  have  a 
similar  flattish  position,  dipping  at  a  low  angle  in  a  general  north- 
erly direction.  Their  present  surface  outcrops  have  a  somewhat 
sinuous  strike  across  the  island.  The  vertical  variations  both 
among  and  within  the  lower  Chazy  beds  are  noteworthy,  and 
there  are  horizontal  variations  shown  in  the  rocks  along  shore, 
which  are  often  accentuated  by  weathering,  but  which  it  is  not 
possible  to  trace  for  any  considerable  distance  inland.  As  a 
whole,  the  Chazy  formation  is  impressive  because  of  the  massive- 
ness  of  its  beds.  This  massiveness  appears  to  be  at  its  maximum 
in  the  limestone  members  of  the  Middle  Chazy.  The  portion  of 
the  Chazy  regarded  as  forming  the  lower  division,  or  Group  A  of 
Brainerd  and  Seely,  seems  to  have  a  larger  visible  extent  on  the 
island  than  any  other  portion  of  the  Chazy.  The  so-called  Middle 
Chazy  is,  however,  widely  exposed.  Outcrops  of  the  upper  por- 
tion are  confined  to  a  relatively  small  area  on  the  east  side  of  the 
island  about  midway  of  its  length.  The  beds  of  this  upper  por- 
tion appear  to  pass  westward  beneath  surface  material,  but  out- 
crops are  lacking  to  show  how  far  it  may  extend. 

About  midway  of  its  length  the  island  is  divided  by  a  low, 
swampy  tract  of  land,  south  of  which  except  for  a  small  strip  of 
shale  along  the  east  shore,  the  visible  rock  all  belongs  to  the 
Beekmantown  or  Chazy.  North  of  this  swampy  land  much  of 
the  island  is  under  clay  or  drift  which  conceals  the  hard  rock 
and  in  these  areas  the  interesting  features  are  the  old  marine 
clays,  the  sea  beaches  with  their  fossils  and  the  drift.  The 
drift  may  be  partly  an  outwash  from  a  readvance  of  the  ice.  In 
it  occur  numerous  shallow  depressions,  now  often  pools  of  water, 
which  suggest  "kettles"  formed  by  stranded  blocks  of  ice.  The 
Pleistocene  deposits  present  a  problem  by  themselves  which  the 
writer  has  made  no  effort  to  work  out. 

Over  the  eastern  part  of  the  northern  half  of  the  island  the 
hard  rock  outcrops  in  many  places  and  apparently  belongs  chiefly 
to  the  basal  Trenton  of  the  region.  How  far  the  members  of  this 
formation  may  extend  beneath  the  surface  covering  to  the  west 
and  north  is  a  matter  for  conjecture.  The  Trenton  rocks  may  be 
traced  by  their  outcrops  over  an  area  about  one  and  a  half  miles 


PLATE  XXII 


Contact  along  a  fairly  regular  and  nearly  vertical  plane 
of  faulting  between  basal  Chazy  with  subjacent  Beek- 
mantown  beds  and  strongly  brecciated  middle  Chazy 
limestone,  at  the  southwestern  end  of  Cloak  (Hill's) 
island,  Isle  La  Motte.     View  looking  north. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  169 

long  and  a  mile  wide.  They  reach  the  east  shore  in  a  few  places, 
but  are  usually  separated  from  the  lake  by  narrow  bands  of  shale 
or  by  the  Black  River.  The  Trenton  rocks  are  rich  in  fossils  and 
in  this  particular  and  other  features  are  much  like  those  in  the 
western  part  of  Grand  Isle. 

At  the  southeast,  north  of  Clarks  Bay,  the  Trenton  beds  are 
separated  from  the  lake  shore  by  a  small  band  of  Black  River. 
There  is  nothing  to  suggest  that  the  Black  River  ever  had  on 
Isle  La  Motte  a  much  greater  extension  in  its  secondary  relation 
to  the  other  rocks  with  which  it  is  now  associated  than  it  has  at 
the  present  time.  As  a  whole  the  Black  River  and  the  Trenton 
beds  lie  in  a  fiattish  position  and  are  not  extremely  deformed. 

The  Black  River  and  Trenton  beds  seem  to  show  with  respect 
to  alteration  differences  from  the  Chazy  similar  to  those  which 
have  been  mentioned  for  Grand  Isle.  The  rocks  of  Isle  La  Motte 
are  clearly  part  and  parcel  of  the  series  to  which  those  of  Grand 
Isle  belong. 

Structure.  The  various  expressions  now  to  be  seen  of 
the  noteworty  deformations  of  the  rocks  on  Isle  La  Motte  are 
to  be  found  chiefly  along  or  near  the  eastern  shore.  Description 
will  begin  with  rocks  at  the  southeastern  end  of  the  island. 

The  gentle  northerly  dip  shown  by  the  beds  at  "The  Head" 
continues  around  the  southeast  shore,  nearly  to  the  small  point 
south  of  Waite  Bay.  After  an  interval  of  about  100  feet  of  sandy 
beach  there  is  shown  an  abrupt  change  of  structure.  The  rocks 
at  the  point  are  greatly  disturbed  and  brecciated.  There  seems 
to  be  an  easterly  dip,  but  from  the  clear  indications  present  of 
severe  compression  this  dip  was  interpreted  as  that  of  a  rough 
jointing  due  to  shearing  and  not  as  that  of  bedding.  The  age  af 
the  rocks  is  uncertain,  but  they  are  probably  some  part  of  the 
Chazy. 

South-southwest  of  Waite  Bay  is  Cloak  Island.  Although 
only  a  few  acres  in  extent  it  possesses  some  very  remarkable 
structural  features.  A  mere  inspection  would  leave  no  doubt 
of  the  fact  that  its  rocks  have  been  under  severe  compression. 

The  rocks  are  apparently  mostly  of  Chazy  age.  A  few  fos- 
sils were  found,  including  Lingula  limitaris  Seely,  and  a  some- 
what plicated  brachiopod  shell  showing  both  valves  with  their 
markings.  In  the  latter,  although  the  beak  was  gone,  other  char- 
acters were  well  preserved.  These  with  the  decidedly  gibbous 
outline  strongly  suggested  Camerotoechia  plena.  Maclurea  has 
been  reported  from  the  west  side  of  the  island,  but  was  not  seen 
by  the  writer.  There  may  be  present  a  small  portion  of  the 
Beekmantown  whose  relations  will  be  described  presently. 

In  the  eastern  part  of  the  island  are  massive  beds  which 
have  clearly  been  folded  and  which  at  some  places  show  westerly 
dip  and  clear  N.-S.  strike.  But  this  mass  deformation  is  masked 
by  severe  brecciation.     The  fragments  of  this  badly  crushed  rock 


170  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

vary  in  size  from  small  bits  to  pieces  two,  three  or  more  feet 
through.  About  midway  of  the  island,  east  and  west,  and  near 
the  south  shore,  a  huge  block  of  house-like  dimensions  rests 
against  the  westward  extension  of  the  brecciated  mass  just  de- 
scribed. In  this  block  the  beds  stand  on  end  with  E.-W.  strike. 
In  them  was  found  the  plicated  shell  referred  to  above.  This 
block  or  mass  is  followed  westward  by  more  brecciated  rock  and 
then  occurs  a  somewhat  detached  mass  of  beds  showing  no  ap- 
parent brecciation  or  shearing.  This  mass  is  perhaps  10  or  12  rods 
long  from  east  to  west  and  5  rods  wide  from  south  to  north.  The 
beds  in  this  mass  all  dip  northerly  at  an  angle  of  about  20  degrees. 
On  the  north  they  are  cut  off  abruptly  by  a  fault  and  rest  along  a 
more  or  less  regular  and  nearly  vertical  plane  (see  Plate 
XXII)  against  coarsely  brecciated  rock  similar  in  this  respect  to 
the  rock  described  for  the  eastern  end  of  the  island.  The  lower 
members  are  much  like  some  of  the  Beekmantown  at  "The  Head" 
on  the  main  island ;  they  are  rather  thickly-bedded  and  often 
weather  to  a  rusty  color.  Above  these  are  other  beds,  perhaps  in 
all  about  15  feet  thick,  with  some  thin,  almost  shaly  members.  At 
the  base  of  this  upper  portion  in  some  sandy  layers  were  found 
a  number  of  fragments  of  Lingula  limitaris  Seely,  which  is 
thought  to  mark  the  base  of  the  Chazy  in  the  Champlain  region. 
The  northwestern  and  northern  parts  of  the  island  are  wooded 
and  outcrops  are  not  satisfactory  for  study.  Along  shore  in 
these  parts  of  the  island  the  rocks  usually  form  steep  cliffs.  On 
the  west  shore  the  rocks  give  the  impression  of  big  blocks  jumbled 
together,  but  they  are  usually  brecciated  on  a  smaller  scale  as 
well.  There  are  indistinct  traces  of  folding  and  indications  that 
in  some  places  the  beds  stand  on  end. 

The  rather  regular  surface  along  which  the  conformable 
northerly  dipping  beds  of  the  southwestern  part  of  the  island 
rest  against  the  coarsely  brecciated  rock  clearly  marks  a  fault.  It 
seems  probable  that  the  brecciated  rocks  are  the  younger  ;  but  what 
was  the  mode  of  deformation  that  brought  these  rocks  into  their 
present  relations  is  far  from  clear.  There  seemed  to  be  no  in- 
dications of  drag  on  any  of  the  exposed  edges  of  the  conformable 
beds.  The  rocks  of  Cloak  Island  and  those  at  the  point  just 
south  of  Waite  Bay  on  the  east  shore  of  the  main  island  give 
every  indication  of  having  been  under  severe  compression. 

Between  the  point  described  above  and  Waite  Bay  on  the 
main  island  are  some  rocks  that  are  apparently  not  much  de- 
formed. Then  along  shore  is  a  short,  sandy  stretch  which  is 
succeeded  northward  by  a  beach  of  bowlders.  Beyond  this  beach 
the  hard  rock  outcrops  along  shore  and  continues  to  Holcomb 
Point.  At  some  places  friable  layers  have  been  cut  by  wave 
action  so  as  to  leave  more  massive  layers  overhanging.  At  other 
places  the  massive  layers  form  the  shore.  South  of  Holcomb 
Point  the  rocks  are  probably  all  Lower  Chazy.     The  layers  are 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  171 

not  appreciably  cieformed.  Similar  rock  occurs  along  part  of 
the  shore  of  the  bay  north  of  Holcomb  Point  and  is  succeeded 
by  beds  whose  age  was  not  determined,  although  they  are  probably 
part  of  the  Chazy. 

About  40  or  50  rods  south  of  Jordan  Point  a  small  bay  shows 
a  narrow  band  of  the  shale  formation,  perhaps  300  yards  long. 
The  rock  is  laminated  like  that  on  the  Alburgh  shore  to  the  east. 
The  dip  of  the  beds,  as  shown  by  the  laminations,  is  prevailingly 
westerly,  but  the  rocks  are  crushed.  North  and  south  along  shore 
the  shale  gives  place  to  limestone,  and  often  the  limestone  forms 
the  higher  part  of  a  bank  which  lower  down  is  composed  of  the 
laminated  shale.  Search  was  made  for  a  contact  between  the 
limestone  and  the  shale  and  what  appeared  to  be  one  was  exposed 
by  digging,  but  the  relation  was  not  decisive  on  account  of  the 
weathered  condition  of  the  shale.  Along  the  shore  where  this 
band  of  shale  occurs  blocks  of  limestone  have  fallen  down  the 
bank  apparently  from  the  action  of  the  waves  upon  the  soft 
shale ;  but  it  is  not  necessary  to  suppose  that  the  limestone  lay  on 
the  shale. 

The  rock  in  the  wooded  pasture  above  the  bank  carries  faint 
coils  of  Madurea  magna,  and  appears  to  be  somewhat  but  not 
severely  sheared.  North  of  the  bay  along  shore  is  massive  Chazy 
carrying  M.  magna  and  Girvanella.  These  Chazy  beds  form  a 
gentle  sag  pitching  northerly  just  north  of  the  bay  and  southerly 
near  Jordan  Point.  The  dip  in  general  is  westerly.  But  along 
this  part  of  the  shore  the  bedding  often  loses  distinctness  or  is 
practically  obliterated  and  the  rock  often  appears  as  a  crushed 
mass  with  fragments  varying  in  size  from  small,  angular  pieces 
to  big  chunks.  At  other  places  instead  of  brecciation  a  shearing 
structure  is  developed  across  the  bedding,  giving  an  impression 
of  easterly  dip.  The  brecciated  rock  occurs  at  the  southern  end 
of  the  band  of  shale  mentioned  above  and  again  north  of  it,  south 
of  Jordan  Point.  Its  outcrops  are  not  extensive,  perhaps  75  feet 
in  the  southern  exposure  mentioned  and  200  feet  south  of  Jordan 
Point.  This  brecciated  rock  may  be  seen  in  contact  with  regularly 
bedded  layers  of  some  of  which  it  may  be  a  part  that  has  been 
crushed.  There  has  been  some  differential  movement  and  disloca- 
tion, but  how  extensive  it  is  difficult  to  make  out.  Perkins  re- 
ported Illaenus  and  Madurea  from  two  separate  fragments  in  the 
breccia.  It  is  interpreted  by  the  writer  as  an  autoclastic  rock. 
The  undeformed  beds  with  which  the  breccia  is  in  contact  seems 
to  be  Middle  Chazy. 

The  low  swampy  tract  extending  from  Clarks  Bay  just  north 
of  Jordan  Point,  westward  across  the  island  probably  is  a  zone  of 
fracture. 

Just  north  of  the  eastern  end  of  this  swampy  tract  Black 
River  beds  form  a  band  along  shore,  perhaps  125  rods  long  and 
10  or  12  rods  wide.     The  beds  of  this  formation  form  a  gentle 


172  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

anticline  at  Hill's  quarry,  dipping  westerly  on  one  side  at  an  angle 
of  about  5  degrees  and  easterly  on  the  other  limb  at  an  angle  of 
about  12  degrees.  Near  the  shore  just  east  of  Hill's  quarry  the 
surface  of  the  rock  shows  many  coils  and  opercula  of  a  Maclurea, 
perhaps  M.  logani,  and  many  small  patches  of  sections  of  shells. 
Except  for  the  Maclurea,  which  was  not  seen  by  the  writer  in 
the  Black  River  elsewhere  in  the  lake  region,  the  rock  closely  re- 
sembles that  which  in  many  parts  of  western  Vermont  has  been 
identified  as  belonging  to  this  terrane. 

For  the  most  part  the  Black  River  beds  are  not  marked  by 
,severe  internal  deformation;  but  at  the  northern  end  of  the  strip, 
at  a  small  point  a  few  rods  south  of  William  Hill's  landing  and 
perhaps  5  rods  north  of  undisturbed  easterly  dipping  beds,  the 
rock  is  crushed  with  development  of  shearing  (see  Plate  XXI). 
This  structure  may  be  best  seen  on  the  north  side  of  the  point  just 
mentioned,  where  the  thick  layers  of  the  Black  River  may  be  seen 
to  form  a  subordinate  anticline  in  which  the  roughly  jointed, 
brecciated  structure  is  particularly  well  shown.  The  bedding  is 
obscured,  but  is  still  visible. 

North  of  the  crushed  Black  River  beds  the  low  bank  and 
shelving  shore  are  for  a  short  distance  in  front  of  the  William 
Hill  place  formed  by  Trenton  beds.  About  50  paces  north  of 
Hill's  landing  along  shore  are  low  ledges  of  a  sheared,  blackish 
rock  which  a  few  steps  northward  forms  a  sharp  headland  in 
which  the  lamination  bands  of  the  shale  are  clearly  shown.  The 
laminations  dip  at  a  high  angle  westerly,  or  are  greatly  broken 
and  fragmented.  The  shale  continues  northward  from  the  head- 
land with  the  dip  changing  direction  in  the  way  so  often  observed 
on  the  islands  lying  to  the  east.  If  not  mashed  the  rock  is 
strongly  sheared  into  a  more  or  less  fissile  condition,  and  is  often 
veined  with  secondary  calcite. 

Perhaps  one-third  of  a  mile  north  of  Hill's  landing  the  shale 
is  interrupted  along  shore  by  a  beach  and  then  occurs  a  small 
mass  of  Trenton  limestone  which  continues  for  about  200  feet. 
After  another  interval  of  beach  the  shale  again  forms  the  shore 
and  continues  along  it  for  perhaps  one-half  a  mile.  Then  the 
Trenton  limestone  outcrops  again  and  extends  to  Cooper  Point. 

In  all  its  exposure  the  shale  forms  only  narrow  strips  on  the 
shore,  but  in  the  most  northern  one  the  rock  may  be  frequently 
seen  in  the  bank  and  at  one  place  it  reaches  across  the  shore  road. 

South  of  Cooper  Point  the  limestone  carrying  Trenton  fossils 
is  at  one  place  folded,  overturned  and  broken  and  a  part  of  the 
rock  has  overridden  another  part.  At  other  places  the  rock  shows 
westerly  dip  and  at  others  lies  nearly  flat.  North  of  Cooper 
Point  the  Trenton  beds  disappear  under  the  shingle  along  shore. 
Around  Cooper  Point  Prasopora  is  abundant,  but  much  altered. 
Strong  compression  is  manifest. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  173 

West  of  the  outcrops  that  have  been  briefly  described  for 
the  east, shore,  between  the  swampy  tract  and  Cooper  Point,  the 
rocks  exposed  in  the  higher  portions  of  the  shore  slopes,  except 
for  some  Black  River  that  has  been  mentioned,  is  all  Trenton  and 
the  Trenton  beds  extend  westward  with  numerous  exposures 
through  the  fields  to  the  main  island  road  running  through  the 
village. 

Away  from  the  shore  the  Trenton  beds  exhibit  less  and  less 
evidence  of  internal  deformation  and  show  a  gentle  northeasterly 
dip  and  northeast  strike.  The  present  topography  of  the  pasture 
land  between  the  shore  and  the  main  island  road  clearly  displays 
the  dip  and  strike  of  the  beds  as  the  land  rises  by  terraces  to  the 
west. 

In  ascending  from  the  shore  to  the  higher  ledges  lying  west 
of  the  camps  along  the  shore  road  fossils  appear,  but  there  is  an 
appreciable  difference  between  these  eastern  outcrops  and  those 
that  lie  farther  west  with  respect  to  the  degree  of  deformation 
and  alteration  of  the  rock.  At  the  east  the  beds  show  clearly  more 
evidence  of  shearing  strain,  with  subordinate  mashing,  although 
the  westerly  dip  is  usually  discernible ;  the  fossils  are  not  well 
preserved. 

The  fossils  in  these  Trenton  beds  west  of  the  camps  include 
the  forms  that  distinguish  the  basal  Trenton  beds  in  the  ridge 
half  a  mile  east  of  the  west  shore  on  Grand  Isle  and  the  rocks 
themselves  are  counterparts. 

To  one  who  examines  this  island  after  a  survey  of  the  island 
of  North  Hero  and  the  peninsula  of  Alburgh  the  scant  occurrence 
of  the  shale  formation  on  Isle  La  Motte  is  impressive.  To  one 
w^ho  may  have  been  inclined  to  the  view  that  the  preservation  at 
the  present  surface  of  broad  areas  of  the  weak  shale  formation,  not 
only  on  the  islands  of  the  lake  but  also  on  the  mainland,  is  perhaps 
due  to  a  covering  until  rather  recent  times  of  a  more  durable 
formation  which  has  been  removed,  the  absence  of  any  traces  of 
rock  that  might  have  served  for  such  protection  anywhere  on 
North  Hero  or  Alburgh  is  also  impressive.  That  such  a  covering 
does  exist  and  probably  has  existed  in  some  places  in  the  lake 
region  may  be  shown ;  but  that  all  the  shales  had  precisely  similar 
thrust  relations  with  massive  limestones  does  not  seem  to  have 
been  the  case. 

But  as  has  already  been  discussed  for  Grand  Isle  and  for 
other  parts  of  the  Champlain  basin  the  region  is  one  eminently 
characterized  by  upthrust  of  older  into  younger  formations.  This 
mode  of  mass  disturbance  is  widely  prevalent  and  conspicuous, 
and  dominates  all  others. 

It  has  also  been  indicated  that  good  evidence  exists  to  show 
that  subsequent  to  the  great  dislocations  that  piled  the  rocks 
against  one  another,  normal  faulting  occurred  by  which  the  rocks 
were  again  fractured  and  displaced.     It  does  not  appear  possible 


174  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

in  many  cases  of  displacement,  both  along  and  across  the  strike, 
to  say  whether  the  dislocation  was  the  result  of  compression  or 
normal  tension  faulting.  In  the  case  of  massive  and  highly 
elastic  limestone  strata  it  is  possible  to  conceive  that  under  com- 
pression the  conditions  might  have  been  such  as  to  permit  a  frac- 
ture across  the  strike  that  would  produce  relations  simulating 
those  that  would  result  from  normal  faulting.  In  the  absence 
of  any  positive  criteria  by  which  the  exact  nature  of  the  differen- 
tial movements  between  masses  now  clearly  lying  in  displaced 
relations  to  one  another  may  be  determined,  the  explanation  of 
such  relations  must  rest  upon  probability. 

The  conditions  on  Isle  La  Motte  are  in  so  many  respects 
comparable  with  those  on  Grand  Isle  that  it  seems  that  an  ex- 
planation which  would  fit  one  would  also  fit  the  other,  and  the 
conditions  that  exist  in  other  parts  of  the  region  are  such  that 
any  interpretation  which  fits  these  two  islands  may  probably  be 
applied  to  the  relations  involving  similar  rocks  at  other  places, 
with  certain  modifications. 

The  absence,  so  far  as  could  be  determined,  of  any  traces  of 
older  limestones  at  the  present  time  on  the  shales  of  North  Hero 
and  Alburgh  stands  against  the  view  that  these  shales  were  ever 
covered  by  such  rocks  and  that  the  massive  limestones  of  Grand 
Isle  and  Isle  La  Motte  represent  downfaulted  blocks  of  a  much 
more  extended  mass  of  such  rocks  that  was  thrust  over  the  shale 
and  which  has  now  largely  disappeared  by  erosion.  This  dis- 
tinctly does  not  mean  that  such  limestones  do  not  now  an'd  never 
did  rest  on  the  shales  at  perhaps  many  places  in  the  lake  region, 
or  that  shales  may  not  underlie  the  massive  rocks  on  Isle  La  Motte 
and  Grand  Isle.  It  further  does  not  mean  that"  the  visible  shales 
of  the  northern  islands  of  the  lake  never  lay  at  some  depth  be- 
neath overthrust  masses.  The  discussion  applies  to  the  relations 
among  the  visible  rocks  of  these  islands. 

The  field  relations  in  the  northern  part  of  the  lake  region 
have  not  after  careful  inspection  seemed  to  favor  the  idea  of 
down-faulting  of  the  shales  among  the  older  limestones  through 
gravitational  stress.  The  field  evidence  everywhere  rather  sug- 
gests that  the  present  relations  shown  between  massive  limestones 
and  shales,  where  the  latter,  as  indicated  by  their  younger  age, 
occupy  the  downthrow  side  of  a  displacement,  are  the  results  of 
compression,  in  spite  of  the  probability  of  normal  'faulting  in  the 
region  and  the  lack  of  positive  proof  of  thrust  contacts.  It  is 
proper  further  to  weigh  the  question  as  to  whether  the  massive 
limestones  of  Grand  Isle  and  Isle  La  Motte  could  have  been  thrust 
into  and  perhaps  over  shales  and  whether  the  field  relations  and 
various  kinds  of  deformation  lend  themselves  to  such  a  view. 

On  the  islands  under  discussion,  there  have  not  been  found 
any  positive  surface  traces  of  overlap  of  older  on  younger  rocks. 
Some  of  the  basal  Trenton  and  associated  Black  River  beds  that 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  175 

occur  at  the  northern  end  of  the  ridge  that  runs  east  of  the  west 
shore  in  the  lower  western  half  of  Grand  Isle  are  older  than  the 
rocks  along  shore  to  the  west  of  them  and  if  normal  faulting  is 
ruled  out  the  topographic  position  and  attitude  of  the  beds  of  the 
former  fall  in  with  idea  of  overthrust.  Contacts  are,  however, 
lacking.  The  lake  waters  conceal  the  hard  rock  that  lies  to  the 
west  of  the  western  shores  of  Grand  Isle  and  Isle  La  Motte  and 
whether  the  shales  come  to  the  surface  beneath  the  lake  is  not 
known.  Farther  south  in  Shoreham  and  Orwell  the  margin  of 
thrust  overlap  of  the  heavy  Hmestones  on  the  shale  may  be  fol- 
lowed at  the  present  surface,  the  shales  lying  to  the  west  of  the 
margin  above  the  lake  water  level. 

On  Grand  Isle,  as  has  been  described,  the  massive  older  rocks 
are  more  or  less  mashed  and  veined  with  calcite  along  their  east- 
ern margin.  It  is  noteworthy  that  the  more  crushed  and  sheared 
condition  of  the  massive  rocks,  both  on  Grand  Isle  and  Isle  La 
Motte,  occurs  along  their  irregular  eastern  margins. 

A  very  similar  condition  has  been  noted  and  described  by 
the  writer  for  certain  rocks  in  the  Hudson  valley.^  Near  Pough- 
keepsie,  N.  Y.,  massive  dolomites  and  limestones  have  field  rela- 
tions to  slates  very  similar  to  the  relations  shown  in  the  lake 
region  and  which  are  plainly  the  results  of  the  older  rocks  having 
been  thrust  into  the  younger  slates.  The  older  beds  have  broken 
both  across  and  along  the  strike  and  in  their  eastern  portions 
often  show  slickensiding  and  brecciation  near  their  contacts  with 
the  slates.*  In  the  Poughkeepsie  region,  along  their  western  mar- 
gins, the  older  rocks  may  often  be  seen  in  contact  with  the  slates 
into  or  over  which  they  have  been  thrust.  It  is  apparent  from 
the  generally  flattish  attitude  of  some  of  these  overthrust  rocks 
and  the  lack  of  deformation  within  them  away  from  the  brec- 
ciated  zone  along  their  eastern  margins  that  they  underwent 
little  folding  and  essentially  form  great  blocks  that  have  been 
broken  from  an  extensive  formation  lying  at  depth  and  driven 
upward.  Although  not  equally  manifest  at  all  places  a  distinct 
horizontal  component  may  usually  be  recognized  in  these  dis- 
placements. Moreover,  what  sometimes  appear  now  as  reverse 
faults  are  probably  eroded  thrusts. 

Taking  the  apparent  absence  of  any  traces  of  the  massive 
Beekmantown,  Chazy  and  Black  River  beds  anywhere  on  Alburgh 
and  North  Hero  at  its  face  value,  it  is  not  reasonable  to  assume 
that  the  shales  in  these  areas  were  overridden  by  a  mass  of  the 
older  rocks  and  that  the  older  limestones  of  Isle  La  Motte  rep- 
resent a  detached  block  of  such  an  overthrust  mass  preserved 
by  downfaulting.  From  the  strong  similarities  which  the  second- 
ary structural  features  in  the  northern  part  of  the  lake  basin 
have  to  those  of  the  Hudson  valley  near  Poughkeepsie,  it  may 
not  be  unreasonable  to  suppose  for  each  of  these  regions  a  similar 

^New  York  State  Bull.  148,  1911. 


176  '    REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

deformational  history.  The  Beekmantown,  Chazy,  Black  River 
and  basal  Trenton  beds  of  Isle  La  Motte  were  broken  from  the  re- 
spective masses  to  which  they  belonged  and  which  lay  beneath  the 
shales  and  have  under  compression,  through  failure  in  any  notable 
degree  to  accommodate  through  close  shearing,  moved  up  into  the 
shale  formation.  By  such  deformation  some  portions  of  the 
shale  would  in  some  measure  probably  have  been  overthrust  and 
other  portions  might  be  spoken  of  as  underthrust.  In  both  cases 
the  shale  would  occupy  the  downthrow  side.  Along  the  plane  of 
underthrust  movement  the  relations  produced  might  sometimes 
suggest  normal  faulting;  but  it  is  clear  that  displacement  due  to 
pressure  would  have  involved  differential  movement  between 
masses  that  were  both  under  compression.  The  shales  accom- 
modated through  cleavage  and  minor  deformation,  but  the  lime- 
stones refusing  to  do  so  moved  as  massive  blocks. 

If  this  interpretation  is  given  to  the  relations  of  the  lime- 
stones of  Isle  La  Motte  to  the  shales,  it  may  be  thought  surpris- 
ing that  the  limestones  are  not  more  generally  present  at  the 
surface  in  nearby  areas.  But  it  is  not  necessary  to  suppose  that 
such  upthrust  masses  had  in  all  cases  the  same  amount  of  dis- 
placement with  respect  to  the  shales.  Probably  at  depth  the 
massive  beds  of  Lower  Ordovician  rocks,  and  probably  older 
rocks  underlying  them,  have  been  variously  broken  and  disturbed. 
The  various  kinds  of  deformation  now  to  be  seen  on  the  eastern 
shore  of  Isle  La  Motte  and  along  what  was  called  the  plane  of 
underthrust  bear  out  the  idea  that  it  was  the  massive  beds  which 
did  the  moving,  so  to  speak.  As  is  so  frequently  to  be  understood 
in  application  to  faulting  and  thrusting,  a  plane  is  not  to  be  thought 
of  as  a  mathematical  plane  but  rather  as  a  zone  of  disturbance. 

At  some  places  it  appears  that  the  limestones  along  the  under- 
thrust side  slid  under  the  shales  at  a  relatively  low  angle  and  at 
Others  ascended  more  nearly  vertically.  The  massive  rocks  were 
all  the  while  crowded  against  the  shales  and  the  crushed  condi- 
tion of  the  latter  is  in  such  wise  not  difficult  to  explain. 

The  thought  has  occurred  that  possibly  the  crushed  condi- 
tion of  the  rocks  as  described  for  the  eastern  shore  of  Isle  La 
Motte  and  for  Cloak  Island  was  a  character  acquired  within  these 
rocks  at  depth  before  actual  rupture  and  extensive  bodily  move- 
ment of  ruptured  masses.  It  certainly  seems  less  likely  that  this 
condition  was  acquired  during  simple  upward  movement  into  the 
shales  after  rupture  from  the  main  mass  at  depth.  The  gradual 
transition  westward  from  strongly  deformed  beds  along  the  east 
shore  of  the  island  through  those  showing  less  and  less  strain  to 
undeformed  beds  seems  to  indicate  that  differential  internal 
deformation  was  followed  by  mass  dislocation. 

The  relations  and  conditions  on  Grand  Isle  are  in  many  par- 
ticulars comparable  with  those  on  Isle  La  Motte  and  it  seems 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  177 

probable  that  the  massive  rocks  of  Grand  Isle  should  be  inter- 
preted as  upthrusts  into  the  shale  formation. 

FRANKLIN  COUNTY. 
Highgate  Township. 

(St.  Albans  topographic  sheet.) 

General.  The  rocks  of  Highgate  have  long  been  known  from 
the  investigations  of  Logan,  who  worked  out  some  of  their  im- 
portant structural  relations.  While  there  have  been  some  modi- 
fications with  advancing  knowledge  of  the  age  relations  assigned 
to  some  of  the  rocks,  the  general  conclusions  of  this  able  geologist 
have  not  been  materially  changed  and  jus  map,  so  far  as  it  went, 
is  accurate  in  detail  of  distribution  and  structure.  The  rocks  of 
the  township  have  been  much  disturbed  and  altered.  Contacts 
are  concealed  and  some  relations  much  obscured  by  the  mantle  of 
surface  material. 

In  Highgate  rocks  are  found  extending  south  from  the 
Canada  line  along  the  lake  shore  and  just  to  the  east  of  it  which 
are  more  or  less  similar  to  those  of  the  areas  just  described  or  to 
some  that  occur  near  the  lake  farther  south  in  Vermont,  but  some 
of  these  rocks  are  greatly  altered.  East  of  a  narrow  and  some- 
what irregular  strip  of  such  rocks  are  others  whose  counterparts 
have  a  great  extension  southward  through  western  Vermont. 
Occurring  among  the  latter  are  still  other  rocks  which  show 
features  different  from  any  of  the  others  and  present  much  diffi- 
culty in  the  definition  of  their  age,  in  their  dorrelation  and  in  the 
explanation  of  their  structural  relationships  to  the  rocks  with 
which  they  are  associated. 

Betzveen  Missisquoi  Bay  and  Rock  River.  Description  will 
begin  with  rocks  along  or  near  the  shore  of  the  lake,  south  of  the 
Canadian  line. 

Just  south  of  the  little  bay  at  the  village  of  Philipsburg, 
Province  of  Quebec,  the  shore  is  formed  of  black,  slaty  rocks 
carrying  graptolites.  These  slates  form  a  narrow,  wave-cut  plat- 
form and  low  cliffs  for  about  a  mile  south  of  Philipsburg.  Ex- 
cept for  their  greater  alteration  and  more  pronounced  cleavage 
and  disturbance  these  rocks  are  much  like  those  of  Alburgh  and 
North  Hero.  They  carry  firm,  siliceous  bands,  weathering  rusty 
brown,  which  from  their  fragmented  condition  and  scattered 
arrangement  among  the  more  shaly  layers  bear  testimony  to  the 
severe  crushing  which  these  rocks  have  suffered.  In  their  de- 
formational  features  these  rocks  are  much  like  those  which  will 
be  described  for  the  lake  shore  south  of  St.  Albans  Bay. 

These  slaty  rocks  are  interrupted  and  replaced  at  places  along 
the  shore  of  the  bay  by  great  cHffs  of  massive-appearing  lime- 
stones which  often  reach  to  the  water's  edge  and  are  impassable 


178  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

except  by  boat.  At  the  bases  of  many  of  these  diffs  are  great 
blocks  which  have  broken  from  them  and  over  which  one  may 
sometimes  scramble  for  considerable  distances  without,  however, 
coming  upon  the  slates.  Working  southward  along  the  tops  of 
these  cliffs  one  comes  to  a  small  bay,  a  little  way  south  of  the 
national  boundary,  in  which  the  slate  outcrops.  Slate  was  observed 
in  the  bank  not  more  than  10  feet  below  the  massive  limestone 
which  caps  it,  but  the  actual  contact  is  concealed.  South  of  the 
bay  the  limestone  reaches  the  water  and  continues  for  many  rods. 
Its  margin  then  recedes  somewhat  eastward  and  clay  or  shingle 
forms  the  shore  with  the  slates  peeking  through  at  places.  Finally 
the  slates  pass  from  sight  towards  Rock  River  Bay. 

The  surfaces  of  the  massive  limestones  which  have  been 
mentioned,  in  the  extension  of  these  rocks  east  from  the  shore 
through  woods  and  pastures  to  the  Highgate-Philipsburg  road, 
were  examined  for  fossils,  but  nothing  definite  was  found.  In 
these  rocks,  which  are  greatly  altered,  fossils  have  apparently 
largely  been  destroyed.  In  the  shore  cliffs  these  limestones 
usually  appear  very  massive,  but  at  some  places  beds  of  not  very 
great  thickness  were  observed.  Sometimes  a  massive  appearance 
seems  to  be  due  to  a  sort  of  welding  of  beds  by  shearing.  Where 
bedding  was  observed  it  showed  easterly  dip  at  a  low  angle. 

The  calcareous  beds  exposed  along  and  near  the  shore  are 
largely  gray,  dolomitic  limestones  distinctly  siliceous  and  often 
carrying  chert,  but  away  from  shore  these  rocks  pass  upward  into 
white,  more  or  less  marbly  limestones  whose  weathered  surfaces 
are  often  covered  with  a  tracery  of  fine  siliceous  lines  of  lace-like 
patterns  standing  out  in  low  relief.  These  whitish  limestones 
outcrop  along  the  Philipsburg-Highgate  road  from  the  national 
boundary  to  and  across  Rock  River  and  form  numerous  expo- 
sures west  of  the  road  in  the  pastures  and  woods.  East  of  Rock 
River  Bay,  both  north  and  south  of  the  stream,  the  white  lime- 
stones were  found  in  close  association  with  the  gray  dolomites 
and  a  similar  association  was  noted  east  of  Highgate  Springs; 
but  at  the  latter  place  there  is  suggestion  of  dislocation  and  at 
one  place  of  westerly  dip  which  is  a  variation  from,  the  rather 
uniform  easterly  dip  shown  by  the  rocks  south  of  the  Canadian 
Hne,  between  the  lake  shore  and  the  valley  of  Rock  River. 

A  mile  east  of  the  shore  near  the  Province  line  are  indications 
of  synclinal  structure  which  becomes  well-marked  two-thirds  of 
a  mile  north  of  the  line.  About  one-fourth  of  a  mile  south- 
southwest  of  St.  Armand  station  and  one-eighth  of  a  mile  west 
of  the  railroad  track,  massive  bluish-gray  and  yellow  weathering 
beds  dip  at  an  angle  of  about  18  degrees  to  the  northwest.  These 
are  succeeded  westward  and  upward  by  massive-appearing  rock 
carrying  fossils,  some  of  which  resemble  Lituites.  This  massive- 
appearing  rock  may  be  seen  to  be  composed  of  relatively  thin 
layers  which  have  been  welded  into  a  thick  stratum,  as  it  now 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  179 

appears.  Some  of  the  rock  shows  a  striped  appearance  in  which 
feature  it  looks  much  Hke  similar  rocks,  which  have  been  thought 
to  belong  to  the  Chazy,  farther  south  in  Vermont.  A  half  mile 
north  of  these  outcrops  along  the  road  from  Moore's  Corners  to 
Philipsburg  the  striped  rock  shows  southeasterly  dip  and  west- 
ward is  underlain  by  the  bluish-gray  and  yellow  weathering  beds. 
The  rocks  in  the  western  limb  of  this  syncline  are  plainly  sheared 
across  the  bedding,  with  the  easterly  dip  of  the  induced  cleavage 
at  a  higher  angle  than  the  bedding.  There  was  observed  at  some 
places  what  was  interpreted  as  a  mashed  structure  as  evidenced 
by  blocks  of  the  yellow  weathering  beds  involved  with  the  dove- 
colored  or  bluish  rock.  Westward  towards  the  shore  are  found 
rocks  like  those  which  have  been  described  as  making  up  most  of 
the  surface  between  the  lake  shore  and  Rock  River  south  of  the 
Province  line,  and  a  generally  low  easterly  dip  is  maintained  in 
these  rocks  to  their  western  margin.  West  from  the  axis  of  the 
syncline  just  mentioned,  the  succession  across  the  strike  in  the 
limestones  is  probably  from  younger  to  older  and  older  rocks. 

These  various  rocks  were  regarded  by  Logan  as  parts  of  his 
Quebec  Group,  a  name  that  now  has  hardly  more  than  historic 
significance.  There  is  still  a  field  for  careful  work  among  these 
rocks  with  regard  to  their  exact  age  and  correlation  and  the  details 
of  their  structure. 

Brainerd  and  Seely  seemed  to  recognize  in  the  Philipsburg 
series  of  Logan  most  of  the  members  of  their  Calciferous  (Beek- 
mantown)  of  Vermont  with  some  beds  that  may  be  Chazy.  The 
identification  was  largely  on  a  lithological  basis. 

These  rocks  have  not  undergone  extensive  deformation  by 
folding.  They  have  suffered  considerable  shearing  and  great 
alteration  from  pressure  and  their  relations  to  the  slates  along 
shore,  than  which  they  are  unquestionably  much  older,  is  that  of 
thrust  which  probably  involved  considerable  lateral  movement. 

Along  Rock  River  valley,  south  of  the  Province  line,  the 
rocks  did  not  give  much  hint  as  to  the  extent  to  which  they  may 
have  been  brecciated  along  their  eastern  margins ;  nor  was  it 
possible  to  determine  if  transverse  and  longitudinal  fractures  are 
present  among  these  massive  limestones  between  the  lake  shore 
and  Rock  River  valley. 

In  their  lithological  features  and  massive  character  these 
dolomites  and  limestones  show  more  resemblance  to  the  similar 
rocks  of  Benson  and  Orwell,  which  the  writer  has  described  in 
relations  to  younger  rocks  quite  like  those  shown  by  the  rocks  of 
Highgate,  than  to  any  other  rocks  which  he  has  seen.  The  gen- 
eral resemblance  is  very  strong  and  seems  to  point  to  a  wide- 
spread substratum  of  similar  rock  which  was  broken  here  and 
there  and  thrust  through  and  over  younger  beds,  in  which  rela- 
tions they  are  now  exposed. 


180  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Highgatc  Springs  and  vicinity.  About  one-half  a  mile  south- 
southwest  of  the  mouth  of  Rock  River  is  Limekiln  Point.  The 
rock  at  this  place  is  a  grayish  limestone  which  has  been  quarried. 
It  is  unlike  the  rock  that  occurs  along  shore  north  of  Rock  River 
Bay,  and  that  to  the  east,  north  of  Carman  Brook. 

Limekiln  Point  is  separated  by  Phelps'  Bay  from  a  blunt 
promontory  lying  to  the  southwest  of  the  Point.  This  promontory 
is  the  site  of  a  former  picnic  ground.  Over  most  of  its  western 
portion  the  rock  is  a  sheared,  impure,  shaly  limestone  which 
forms  low  cliffs  along  the  edge  of  the  lake.  These  impure  lime- 
stones yielded  somewhat  distorted  fossils,  among  which  some 
were  sufficiently  well  preserved  to  warrant  the  following  tentative 
references : 

Rafinesquina  incrassata  (Hall) ;  compare  Leptaena  plicifera  Hall, 
fig.  la,  pi.  4  bis,  Pal.  N.  Y.  1847. 

R.  incrassata,  but  larger  than  preceding,  showing  convex?  valve 
with  narrow  and  fairly  deep  depression  extending  from  beak  to  margin, 
widening  somewhat  towards  margin. 

R.  fasciata.  comparable  in  size  with  fig.  3c  and  in  detail  with  figs. 
3a  and  3d,  pi.  4  bis,  loc.  cit. 

The  smaller  specimen  compared  with  R.  incrassata  has  some  re- 
semblance to  certain  illustrations  of  the  dorsal  valve  of  Plectambonites 
sericeus  (Sowerby),  but  differs  in  proportions,  being  shorter  along  the 
hinge  line.  The  striae  are  also  coarser,  fewer  in  number,  and  of  uni- 
form size,  with  intermediate  ones  appearing  near  the  margin.  The 
specimen  referred  to  R.  fasciata  is  comparable  with  R.  alternata, 
(Emmons).  A  gastropod  of  EccuUomphalus  type  was  also  seen.  The 
specimen  was  badly  worn,  but  in  spite  of  excoriation  seemed  to  show, 
particularly  near  the  tip,  low,  annular  ridges.  There  was  no  visible 
angulation. 

These  fossils  suggest  that  the  shaly  limestone  may  be  of  Upper 
Chazy,  or  possibly  Trenton  age.  These  limestones  are  flanked  on 
the  east  by  certain  less  sheared  calcareous  rocks  that  are  in  turn 
overlain  by  beds  that  resemble  the  Black  River.  Portions  of  the 
shaly  limestones  are  less  sheared  than  others,  but  most  of  these 
rocks  under  the  hammer  break  into  irregular  pieces  whose  surfaces 
are  suggestive  of  slight  movements  in  the  rock.  In  fact,  the  condi- 
tion of  most  of  these  shaly  rocks  is  substantially  that  of  irregular 
cleavage  or  crushing. 

The  shaly  limestones  just  described  occur  on  the  east  side  of 
the  road  running  north  from  the  Franklin  House  to  the  wharf  on 
the  second  promontory  southwest  of  Phelps'  Bay,  and  about  a 
half  mile  north  of  the  hotel.  In  spite  of  shearing  an  easterly  dip 
is  apparent.  These  rocks  are  succeeded  westward,  on  the  west 
side  of  the  road,  by  interbedded  gray  limestones  and  buff-weather- 
ing dolomites  which  are  well  shown  at  the  end  of  the  promontory. 
Flanking  these  limestones  and  dolomites  on  the  west  and  ap- 
parently conformable  with  them  are  purplish  or  greenish-gray 
quartzitic  sandstones  in  beds  from  2  to  12  inches  thick  standing 
on  end.     The  quartzitic  sandstones  are  perhaps  a  hundred  feet 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  181 

thick.  South  and  west  they  give  place  to  younger  rocks,  from 
which  they  are  probably  separated  by  a  dislocation.  The  sand- 
stones form  the  western  limb  of  a  broken  anticline.  It  is  not 
clear  just  what  the  relation  of  the  shaly  limestones  is  to  the  inter- 
bedded  gray  and  buff- weathering  beds  that  lie  west  of  them ;  they 
apparently  lie  above  them. 

The  promontory  bounded  on  the  west  by  the  sandstones  is 
separated  by  a  slight  embayment  of  the  shore  from  a  small  point 
at  which  occurs  a  series  of  very  dark  gray  or  blackish,  thinly- 
bedded  limestones  which  gave  good  Trenton  fossils.  In  fossils 
and  general  lithology  these  Trenton  rocks  are  comparable  with 
the  basal  Trenton  beds  as  seen  on  the  islands  to  the  southwest. 
They  are  folded  and  sheared.  They  grade  into  more  shaly  rocks 
which  outcrop  in  the  bank  and  along  the  beach  below  the  camps 
southward  until  lost  under  the  swampy  land.  Eastward  above 
the  bank  in  the  fields  among  the  summer  cottages  the  Trenton 
beds  are  associated  and  folded  with  dense,  black  limestones  of 
probably  Black  River  age.  These  rocks  continue  southward, 
forming  a  ridge  to  the  west  of  the  Highgate-Swanton  road. 
About  one-fifth  of  a  mile  south  of  the  hotel  they  form  an  un- 
symmetrical  anticline  with  the  Black  River,  forming  the  eroded 
crest  and  the  Trenton  beds  the  eastern  and  western  limbs.  On 
the  east  limb  a  reading  gave  the  strike  as  N.  28°  E.  and  the  dip 
about  25°  to  the  east.  The  Trenton  rocks  yielded  typical  fossils. 
On  the  west  limb  the  beds  dip  at  a  high  angle  to  the  west  or  are 
overturned.  About  a  half  mile  south  of  these  outcrops  and  about 
on  the  same  meridian  a  small  ridge  in  the  field  west  of  the  road 
shows  the  western  limb  of  an  anticline  with  the  Trenton  and 
Black  River  beds  in  inverted  position.  The  Black  River  beds  are 
from  2  to  3  feet  thick  and  filled  with  small  calcite  veins,  which, 
it  may  be  noted,  are  frequent  in  all  the  beds  of  this  formation 
around  Highgate  Springs  as  they  are  in  many  other  places  in 
western  Vermont.  The  Trenton  beds  follow  the  Black  River  con- 
formably on  th^  west  and  dip  at  the  same  high  angle  easterly. 
The  Trenton  beds  yielded  crinoid  stems  and  fragments  of  other 
fossils.  Southward  these  rocks  pass  under  surface  material ; 
the  most  southerly  outcrop  noted  in  Highgate  occurs  where  the 
Highgate-Swanton  road  crosses  the  railroad  track. 

Directly  east  from  the  Franklin  House,  across  the  track  near 
the  mineral  spring,  beds  carrying  Trenton  fossils  (Cryptolithus) 
dip  to  the  east.  These  outcrops  are  separated  by  a  stretch  of 
low,  flat  land  about  one-fourth  of  a  mile  wide  from  the  massive 
limestones  in  the  quarries  of  the  Missisquoi  Lime  Works.  To  the 
south  and  southeast  is  an  extensive  sand  plain  under  which  the 
hard  rocks  are  largely  concealed.  _  Just  north  of  the  Swanton 
line  and  a  mile  northeast  of  Swanton  village,  the  road  from  Swan- 
ton  to  Highgate  Center  crosses  a  low  ridge  of  dove-colored  lime- 


182  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Stone  carrying  patches  of  buff-weathering  rock.  These  beds  seem 
to  be  Hke  those  at  the  promontory  at  Highgate  Springs. 

Structural  Features  at  Highgate  Springs.  In  conformity 
with  their  less  massive  characters  the  various  rocks  around  High- 
gate  Springs  have  been  much  more  deformed  by  folding  than 
have  the  heavy  dolomites  and  limestones  that  lie  north  and  east 
of  them.  The  folding  is  distinguished  by  a  tendency  to  over- 
turning on  the  western  limbs  and  actual  inversion  of  beds  in 
some  cases.  Although  now  seen  to  be  disposed  for  the  most 
part  in  folds  the  relations  in  some  places  indicate  dislocations. 
The  Chazy  rocks  have  ridden  on  the  Trenton  and 'the  latter  has 
probably  been  thrust  against  younger  slates.  Shearing  structure 
in  the  form  of  brecciation  or  cleavage  is  to  be  seen  in  many  of 
the  rocks.  The  more  massive  rocks  show  fewer  distinct  marks 
of  internal  deformation. 

Between  the  rocks  at  Limekiln  Point  and  Highgate  Springs 
and  those  lying  to  the  east,  north  of  Carman  Brook,  as  well  as 
those  lying  practically  on  the  same  meridian  with  the  latter  in 
the  westernmost  quarry  of  the  Missisquoi  Lime  Works,  there  is 
an  interval  of  surface  material  so  that  it  is  not  possible  to  state 
what  are  the  contact  relations  between  the  rocks  lying  at  the  east 
and  those  nearer  the  lake.  But  there  can  be  no  doubt  that  the 
massive  rocks  along  the  lake  north  of  Highgate  Springs  rest  on 
the  slates  by  thrust  and  it  is  probable  that  the  rocks  at  Limekiln 
Point  and  Highgate  Springs  are  separated  from  the  altered 
massive  rocks  to  the  east  of  them  by  a  plane  of  thrust,  and  that 
the  present  sinuous  western  marginal  outcrop  of  the  rocks  lying 
east  of  Highgate  Springs  and  north  of  Carman  Brook  is  essen- 
tially a  continuation  of  the  obvious  margin  of  overlap  of  the 
similar  rocks  on  the  slates  north  of  Rock  River  Bay. 

According  to  this  view,  the  folded,  overturned  and  broken 
strata  at  Highgate  Springs  and  those  of  Limekiln  Point  probably 
represent  an  aborted  thrust  which  developed  only  to  the  point  of 
release  of  other  rocks  by  rupture.  These  other  jocks  might  not 
be  those  which  now  form  the  surface  east  of  the  margin  of  over- 
lap discussed  above,  but  might  be  other  rocks  that  are  now  covered 
by  these  thrusted  rocks.  Such  a  view  depends  upon  the  idea  of 
repeated  minor  thrusts  or  reverse  faults  preceding  other  thrusts. 
Exposure  of  rocks  younger  than  the  massive  limestones  has  not 
been  accomplished  east  of  the  margin  of  overlap  of  the  latter  in 
this  part  of  Vermont  and  all  sections  east  of  this  margin  gives  a 
succession  from  younger  to  older  formations,  at  least  as  far  east 
as  the  eastern  valley  of  Rock  River. 

An  alternative  explanation  seems  to  be  that  the  rocks  at 
Highgate  Springs  and  Limekiln  Point  may  have  ridden  forward 
on  the  same  major  shear  with  the  more  altered  rocks  lying  to  the 
east  and  that  the  present  trace  of  this  shear  at  Highgate  Springs 
is  on  the  west  of  the  rocks  at  this  place.     This,  however,  assumes 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  183 

that  a  major  shear  cut  minor  thrusts  and  faults  at  depth  and 
drove  the  truncated  portions  forward  together.  It  is,  of  course, 
not  possible  to  decide  the  point. 

In  every  case  where  a  marked  dislocation  occurred  it  is  to  be 
attributed  to  the  more  or  less  massive  character  of  the  rock  and 
its  reluctant  behavior  under  powerful  compression.  The  rocks 
behaved  according  to  the  elements  of  their  primary  structure. 
The  heavy  members  moved  as  masses ;  the  less  massive  accom- 
modated by  folding,  crushing  and  shearing  on  a  minor  scale. 

Northeast,  east  and  southeast  of  Highgate  Springs.  Rock 
River  has  a  roundabout  course  from  its  source  to  Lake  Cham- 
plain.  Its  upper  eastern  portion  flows  northerly  in  a  course 
roughly  parallel  with  the  shore  of  Missisquoi  Bay  and  about  three 
miles  distant  from  it.  The  river  crosses  the  Province  line  and 
about  two  miles  north  of  it  turns  west  across  the  structural  axes 
of  the  hard  rocks  and  then  bends  to  a  southwesterly  direction  to 
enter  the  lake. 

Part  of  the  rocks  to  be  described  under  the  above  heading 
lie  between  the  northward  and  southward  courses  of  the  river  as 
it  touches  Vermont  and  the  rest  are  found  in  the  territory  that 
extends  southward  and  southwestward  toward  the  Highgate- 
Swanton  line. 

Along  the  eastern  margin  of  the  valley  of  the  lower  (west- 
ern) portion  of  Rock  River  is  a  modified  escarpment  in  a  series 
of  interbedded,  usually  massive,  siliceous  dolomites,  and  quartzites 
or  quartzitic  sandstones,  which  belong  to  so-called  Red  Sandrock 
series,  as  this  formation  was  named  by  the  early  geologists  of 
Vermont.  The  western  outcrop  of  these  rocks,  beginning  at  the 
Canada  line,  follows  rather  closely  for  a  distance  of  about  three 
miles  the  road  that  runs  from  St.  Armand,  P.  Q.  southward  past 
Saxe  monument  to  Swanton.  For  the  rest  of  its  course  through 
Highgate  the  western  margin  is  much  less  distinct  and  usually 
may  be  only  approximately  located  from  a  few  isolated  outcrops 
emerging  through  the  sand  plain.  .  The  most  western  outcrop 
noted  in  Highgate  was  in  a  bed  of  quartzite  at  Kelly  Brook, 
where  this  stream  is  crossed  by  a  road  one  mile  east  of  the 
Central  Vermont  railroad  track. 

Over  the  higher  land  north,  east  and  south  of  Saxe  monu- 
ment the  members  of  this  series  are  well  displayed.  Outcrops  are 
abundant  along  the  roads  and  in  the  fields  nearly  to  the  eastern 
valley  of  Rock  River,  and  the  series  was  traced  southward  along 
the  eastern  edge  of  the  sand  plain  through  Carter  Hill  to  a  point 
just  north  of  the  St.  Johnsbury  and  Champlain  railroad  and 
about  a  mile  west  of  Highgate  Center. 

The  members  of  the  Red  Sandrock  series  in  Plighgate  form 
only  a  small  portion  of  a  great  band  of  more  or  less  similar  rocks 
that  extends  for  a  long  distance  southward  in  Vermont.  Even 
in  rather  widely  separated  areas  in  the  northern  part  of  the  state 


184  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

there  is  close  resemblance  in  sequence  and  thickness  of  beds  of 
this  formation  and  in  their  colors,  but  in  other  places  in  Vermont 
the  members  of  the  Sandrock  series,  are  seemingly  represented  by 
rocks  which  are  apparently  so  unlike  them  that  their  common 
membership  in  the  same  formation  is  easily  overlooked.  Even 
within  short  distances,  however,  the  members  of  the  typical  Sand- 
rock  series  show  appreciable  horizontal  and  vertical  variations  in 
lithological  characters  and  thickness  of  beds  which  come  out  in 
tracing  the  formation  from  place  to  place.  At  many  places  these 
rocks  show  much  confusion  on  account  of  disturbances  which 
have  brought  them  into  abnormal  relations  with  other  rocks ;  but 
leaving  out  dislocations  it  would  not  be  possible  to  describe  any 
vertical  section  which  would  hold  in  detail  for  any  great  distance 
away  from  the  locality  selected. 

It  seems  probable  from  studies  that  have  now  been  made  in 
various  parts  of  western  Vermont,  reckoning  with  the  principle 
of  lateral  variation  among  rocks  of  the  same  general  age,  that 
ideas  about  the  age  relations  of  some  rocks  will  have  to  be  revised. 
It  seems  likely  too,  in  view  of  deformations  of  the  rocks,  that 
estimates  of  the  thicknesses  of  some  of  them  will  have  to  be 
modified.  When  the  general  similarity  in  field  relations  shown 
by  very  different  looking  rocks  is  appreciated  even  the  absence 
of  fossils  in  some  of  them  may  not  stand  in  the  way  of  recogni- 
tion of  the  existence  of  a  formational  unit  whose  depositional 
and  deformational  histories  have  been  much  the  same  throughout. 

In  Highgate  the  members  of  the  Sandrock  formation  require 
only  brief  description.  It  would  require  long  and  patient  work 
to  catalogue  all  the  minor  variations,  which  when  done  would 
largely  represent  wasted  effort  from  our  point  of  view.  How- 
ever, when  the  depositional  history  of  the  Lower  Cambrian  in 
Vermont  is  written  it  will  mean  that  much  attention  will  have 
been  given  to  details  of  such  kind. 

South  and  east  of  Saxe  monument  are  more  or  less  massive 
quartzites,  often  weathering  to  a  rusty  color,  apparently  passing 
along  the  strike  into  reddish  quartzites,  and  eastward  across  the 
strike,  towards  Saxe  Brook,  into  whitish  quartzites,  all  more  or 
less  regularly  interbedded  with  gray,  siliceous  dolomites.  The 
quartzites  are  all  more  or  less  calcareous  or  dolomitic. 

North  of  Saxe  monument  are  gray,  dolomitic  quartzites  and 
siliceous  dolomites  passing  eastward  into  flaggy  quartzites.  A 
gray,  rusty-weathering,  impure  quartzite  east  of  the  St.  Armand 
road  and  about  100  rods  northeast  of  the  monument  gave  recog- 
nizable fragments  of  the  glabella,  cheeks  and  pygidium  of 
Olenoides  marcoui.  These  were  the  only  fossils  found  by  the 
writer.  In  these  rocks  fossils  come  out  only  when  the  rock  has 
weathered ;  but  as  experience  will  show  not  all  weathered  rock 
gives  fossils,  although  it  is  probable  that  these  are  very  common 
in  the  rocks. 


.      REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  lyS 

Southeastward  toward  Highgate  Center  are  brownish-gra}^ 
quartzites  and  gray  dolomites  interbedded  with  flaggy  quartzites. 

In  almost  all  the  outcrops  noted  the  dip  is  at  a  moderate  angle 
to  the  east.  * 

As  a  whole,  these  rocks  probably  make  up  a  considerable,  but 
as  yet  undetermined,  thickness  of  Lower  Cambrian  beds,  showing 
a  rather  uniform  easterly  dip  and  hardly  any  evidence  of  folding. 
The  topography  gives  an  occasional  hint  of  dislocation ;  about  one 
mile  east  of  Saxe  monument,  east  of  Saxe  Brook,  a  prominent 
scarp  in  massive  quartzite  probably  marks  a  fault. 

The  rocks  of  the  Sandrock  series  are  unquestionably  older 
than  the  massive  limestones  that  lie  west  of  them  along  and  east 
of  the  shore  of  Missisquoi  Bay.  The  only  reasonable  explana- 
tion of  their  structural  relations  is  that  which  Logan  advanced 
long  ago;  the  Sandrock  has  been  thrust  against  the  limestones. 
Whether  the  thrust  carried  the  Lower  Cambrian  any  considerable 
distance  over  the  massive  limestones  cannot  be  determined  from 
the  relations  in  Highgate.  No  contacts  were  found,  but  about  a 
mile  southwest  of  Saxe  monument  a  quartzite  bed  of  the  Sand- 
rock series  is  in  close  proximity  to  rocks  of  the  lake  shore  series. 
Outcrops  that  were  seen  in  the  sand  plain  southeast  of  Highgate 
Springs  show  the  margin  of  the  Sandrock  to  be  farther  west 
than  it  is  at  the  north. 

In  their  deformation  the  Lower  Cambrian  beds  behaved 
like  the  massive  limestones  to  the  west  of  them.  While  they 
probably  suffered  subordinate  dislocations  which  are  not  now 
generally  recognizable,  they  did  not  fold  much  but  rather  moved 
as  a  mass. 

In  their  lack  of  folding  the  members  of  the  Sandrock  series 
in  Highgate  are  in  contrast  to  some  of  the  similar  rocks  found 
farther  south  in  Vermont,  which  are,  however,  when  folded,  in 
thinner  beds.  In  their  lack  of  this  kind  of  deformation  they  are 
in  accord  with  similar  heavy  beds  elsewhere.  The  rocks  behaved 
under  pressure  according  to  the  elements  of  their  primary  struc- 
ture. 

In  Highgate  the  Lower  Cambrian  series  is  nowhere  in  visible 
contact  with  the  shale  formation  as  it  is  farther  south  on  the 
lake  shore.  But  what  the  relations  may  be  beneath  the  sand 
plain  that  intervenes  between  Highgate  Springs  and  Swanton  the 
surface  covering  effectually  hides. 

Eastern  valley  of  Rock  River.  Along  the  eastern  valley  of 
Rock  River,  or  low  on  the  eastern  flanks  of  the  hills  of  inter- 
bedded quartzites  and  dolomites  that  have  just  been  described, 
occur  outcrops  of  rocks  very  different  from  the  members  of  the 
Lower  Cambrian  series  that  bounds  them  on  the  west  and  from 
rocks  that  lie  immediately  to  the  east.  These  rocks  show  inter- 
esting differences  among  themselves  from  place  to  place  and  in 
the  same  outcrop,  but  have  a  general  resemblance  to  each  other 


186  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

throughout  and  appear  to  make  up  a  formational  unit.  They 
form  the  northern  extension  of  the  formation  which  includes  the 
so-called  "intraformational  conglomerate,"  described  by  Edson 
for  the  towns  of  Swanton  and  St.  Albans,  and  which  he  was 
inclined  to  view  as  of  Middle  Cambrian  age.  Logan  showed 
these  rocks  on  his  map  (Atlas  accompanying  Geology  of  Canada, 
1863)  as  a  band  extending  northward  from  Highgate  Center 
across  the  Province  line  and  as  joining  at  the  surface  with  his 
Quebec  rocks  in  southern  Stanbridge.  Along  Rock  River  these 
rocks  as  now  exposed  seem  to  hold  to  a  fairly  uniform  width  and 
band-like  distribution,  usually  less  than  a  mile  in  breadth  across 
the  strike  and  sometimes  very  narrow.  Their  representatives 
farther  south  are  often  more  scattered  and  irregular  in  distribu- 
tion. 

This  formation  was  traced  to  within  a  half  mile  of  the 
Canadian  line.  At  an  exposure  near  the  junction  of  the  roads 
about  a  mile  and  a  half  east-northeast  of  Proper  Pond  are  thinly- 
bedded,  bluish  limestones,  whose  outcropping  edges  along  their 
strike  appear  as  wavy  bands  on  the  weathered  surface  of  the 
ledge.  The  limestone  is  associated  with  siliceous  beds  which  lie 
on  it  and  appear  to  be  conformable,  as  though  interbedded.  Con- 
glomeratic structure  is  not  prominent,  being  confined  to  a  patch 
about  four  feet  square.  However,  the  field  was  not  exhaustively 
examined  at  this  locality. 

The  valley  of  Rock  River  is  more  or  less  filled  with  drift 
and  outcrops  are  intermittent.  The  next  outcrops  noted  are  one- 
third  of  a  mile  to  the  south,  west  of  the  road  running  parallel  to 
the  river.  At  this  place  the  thinly-bedded,  bluish  limestone  is 
intermingled  with  slaty  rocks. 

About  a  mile  farther  south,  near  the  junction  of  three  roads, 
are  outcrops  of  sheared,  bluish  limestone,  weathering  to  a  dull 
gray.  The  rock  is  splintered  and  at  places  shows  small  disloca- 
tions which  have  completely  severed  the  thin  beds  at  numerous 
places. 

Southward  where  the  road  crosses  the  river,  in  the  bed  of 
the  stream,  are  sheared  limestones  now  practically  limy  slates. 
The  bedding  is  largely  obliterated  by  the  cleavage  which  dips 
easterly.  The  exposure  of  these  rocks  in  the  river  bed  may  be 
50  yards  in  breadth. 

Above  the  river  bank,  southeastward,  in  a  field  east  of  the 
road,  is  a  curious  mixture  of  rocks  which  in  general  aspect  are 
very  like  those  making  up  several  exposures  in  the  towns  of  Swan- 
ton  and  St.  Albans,  to  be  described  later.  In  fact  the  rocks  at 
these  several  separated  localities  are  counterparts,  so  far  as  litho- 
logical  features  go.  The  most  conspicuous  member  is  the  con- 
glomerate whose  fragments  range  in  size  from  small  pieces  to 
considerable  blocks  and  are  imbedded  in  a  calcareo-siliceous 
matrix.  The  conglomerate  portions  are  intermingled  with  other 
rocks,   some  of  which  are  calcareous  sandstones  much  like  the 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  187 

matrix  of  the  conglomerate,  and  which  sometimes  weather  to  a 
reddish  bluff,  and  others  are  slaty  rocks  like  those  in  the  river  bed 
nearby.  The  fragments  of  the  conglomerate  are  frequently 
bluish  limestone  and  often  sharply  angular  in  section.  There  is 
much  confusion  and  anything  like  orderly  sequence  was  not  dis- 
cernible.    There  is  visible  shearing  structure  in  some  of  the  rocks. 

A  half  mile  farther  south,  where  the  road  crosses  the  river, 
near  Johnson's  farm,  is  a  gorge  worn  by  the  stream  in  dark, 
bluish-gray,  finely  granular  limestone  which  yielded  obscure  fos- 
sils, too  fragmentary  for  positive  determination,  including  a  tiny 
orthis-like  form  and  several  pieces  of  trilobites,  all  very  small. 
The  rock  shows  folding  and  shearing  and  some  brecciation.^ 

Twenty-five  rods  southwest  of  the  bridge  at  the  last-named 
locality  and  west  of  the  road,  at  a  small  ridge,  are  excellent  ex- 
posures of  the  thinly-bedded,  bluish  limestones  like  those  de- 
scribed for  the  outcrops  farther  north.  The  edges  of  the  beds 
show  a  very  conspicuous  wavy  arrangement  and  the  layers  show 
all  stages  of  fragmentation  or  dislocation  from  incipient  parting 
to  rupture  with  varying  degrees  of  displacement  of  broken  parts. 
According  to  the  writer's  view,  these  are  distinctly  secondary  com- 
pression effects,  belonging  in  the  category  of  brecciation,  and  not 
to  be  confused  with  conglomeratic  structure  which  parts  of  this 
formation  show.  The  angular  character  of  the  conglomerate  frag- 
ments often  gives  a  distinctly  brecciated  appearance  to  that  rock 
in  many  of  its  outcrops  and  the  fragments  themselves  often  sug- 
gest broken-up,  thin,  limestone  layers ;  but  the  principal  structure 
of  the  conglomerate  proper  seems  really  to  be  primary,  although 
the  way  it  was  produced  remains  a  mystery.  The  conglomerate 
itself  may  show  secondary  shearing  effects  like  some  of  those  in 
the  rocks  associated  with  it. 

Blue  limestones  like  those  in  the  ridge  just  mentioned  con- 
tinue southward  on  the  strike  and  outcrop  on  the  road  going  west, 
along  which  road  after  an  interval  of  drift  they  are  succeeded 
by  the  Cambrian  dolomites  and  quartzites. 

Highgafe  Center.  In  a  cut  of  the  St.  Johnsbury  and  Lake 
Champlain  R.  R.  one-fourth  of  a  mile  northwest  of  the  village  of 
Highgate  Center  is  exposed  a  laminated  bluish  limestone  dipping 
easterly  at  a  moderate  angle  and  cut  by  rough  shearing  joints 
which  dip  in  the  same  direction  at  a  high  angle.  The  rock  has 
weathered  enough  to  bring  out  the  essentially  shaly  character  of 
the  rock  by  the  laminations  bands  which  it  shows. 

The  field  south  of  the  cut,  above  the  bank,  gives  numerous 
exposures  of  the  thin,  blue  limestones  noted  along  the  valley  of 
Rock  River.  The  beds  sometimes  stand  at  a  high  angle  of  dip 
and  present  the  same  wavy  arrangement  in  the  surface  of  the 
ledge.  The  limestones  are  intermingled  with  ledges  of  gray 
slates.     All  the  rocks  are  greatly  altered  and  without  fossils. 

^  See  supplementary  note  at  the  end  of  this  paper. 


188  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Highgate  Falls.  At  Highgate  Falls  the  Missisquoi  River 
flows  through  a  narrow  post-glacial  channel  which  the  stream  has 
cut  in  a  mass  of  jumbled  rocks  now  exposed  in  its  bed  and  banks. 
The  section  from  the  bridge  to  the  final  outcrops  at  the  base  of 
the  falls  is  perhaps  one-fifth  of  a  mile  long  and  practically  cuts 
the  rocks  from  east  to  west  across  their  strike.  The  gorge  lies 
about  one-half  mile  south  of  the  laminated,  dark  blue  limestone 
and  thin,  lighter  blue  limestones  and  intermingled  slates,  described 
above  for  the  locality  just  northwest  of  Highgate  Center  village, 
and  about  two  miles  north-northwest  of  the  northern  exposures 
in  Swanton  township  of  the  thin  limestones,  shales  and  con- 
glomerate which  outcrop  along  the  Highgate-St.  Albans  road. 

In  the  upper  part  of  the  northern  wall  of  the  gorge  just  below 
the  bridge  is  a  massive  looking  stratum  of  dark,  fine-grained, 
siliceous  rock,  twenty  or  more  feet  thick  as  now  exposed,  which 
may  be  seen  to  have  suffered  some  shearing,  and  which  as  a 
whole  shows  little  evidence  of  bedding.  In  the  lower  portion  of 
this  stratum  is  a  curious  "breccia"  of  small  blocks  of  slaty  rock, 
angular  in  section  and  imbedded  in  a  matrix  of  dark,  fine-grained 
material.  About  75  feet  below  the  bridge,  in  the  base  of  the 
massive  stratum,  is  included  a  large  block  of  somewhat  banded, 
coarse-textured  slate  in  a  piece  of  which  were  found  two  ill-pre- 
served specimens  of  graptolites,  tentatively  identified  by  the  writer 
as  Dictyonema,  probably  flabelliforme,  and  Staiirograptus  dicho- 
tomus  Emmons. 

The  occurrence  of  these  bryograptoid  forms  at  this  locality  is 
worthy  of  note.  The  specimens  were  submitted  to  Dr.  Ruede- 
mann  of  Albany.  While  recognizing  their  poor  state  of  preserva- 
tion, Dr.  Ruedemann  felt  sufficiently  sure  of  the  general  affinities 
of  these  fossils  to  write :  "Even  lacking  a  correct  specific  de- 
termination of  the  forms,  it  is  safe  to  say  that  they  belong  either 
to  the  Schaghticoke  or  Deep  Kill  shales  (Hudson  valley  forma- 
tions) for  the  higher  graptolite  shales  of  the  slate  belt  do  not 
afford  similar  species."  In  specific  reference  to  the  opinion  of 
the  writer  as  to  the  forms  to  which  these  fossils  might  be  referred, 
or  with  which  they  might  at  least  be  compared,  Dr.  Ruedemann 
wrote :  "The  fossil  which  you  compare  with  Staiirograptus 
dichotomus  has  indeed  the  general  aspect  and  outline  of  that 
species.  On  closer  inspection,  however,  it  appears  to  be  rather  a 
young  Dictyonema,  flattened  out  in  a  vertical  instead  of  a  lateral 
direction.  This  conclusion  is  suggested  both  by  the  Dictyoncma- 
like  appearance  of  the  thecae  and  the  apparent  presence  of  dis- 
sepiments connecting  the  branches.  The  fossil  marked  (2)  is  a 
fragment  of  Dictyonema,  possibly  of  the  flabelUforme-group,  but 
also  comparable  to  D.  rectilineatum  of  the  Deep  Kill  shale." 

Dr.  Ruedemann  had  no  knowledge  of  the  specific  locality  at 
which  these  fossils  were  found.     His  properly  guarded  and  yet 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  189 

reasonably  confident  judgment  that  they  probably  represent  a 
Beekmantown  horizon  is  of  interest. 

The  question  would  at  once  be  raised  as  to  the  probable  ex- 
tent at  Highgate  of  the  formation  to  which  these  fossiliferous 
slates  belong.  This  it  would  be  difficult  to  state.  In  the  gorge 
the  rocks  change  in  lithological  character  within  short  distances. 
The  particular  block  yielding  the  fossils  seems  to  be  somewhat 
isolated,  although  similar  rock  appears  to  form  part  of  the  river 
bed  adjoining  the  wall  of  the  gorge.  The  rock  carrying  the  fossils 
gives  place  rather  abruptly  westward  to  the  brecciated  rock  de- 
scribed above  as  forming  the  basal  portion  of  the  massive  stratum 
and  which  also  forms  part  of  the  river  bed  adjoining  the  wall. 

The  section  passes  vertically  downward  from  the  "breccia" 
into  a  mass  of  jumbled  grayish-black,  or  sometimes  bluish-black 
slates  carrying  firmer  bands  of  yellow-weathering  rock.  The 
slates  are  strongly  sheared  and  the  included  firmer  bands  are 
usually  twisted  or  broken  so  that  large  detached,  more  or  less 
rectangular  blocks,  as  the}?^  appear  on  the  surface,  now  lie  in 
helter-skelter  fashion  among  the  slates,  often  oriented  across  the 
strike  at  various  angles.  The  disturbances  which  the  slates  have 
suffered  interfere  with  any  reading  of  the  dip  of  the  bedding  and 
the  thickness  exposed  remained  undetermined.  Close  inspection 
of  the  surface-  of  the  slate  at  many  places  reveals  the  presence 
of  small  fragments  of  slate  very  similar  to  their  matrix,  the  whole 
so  thoroughly  compacted  that  the  broken  up  condition  is  hardly 
visible  except  at  close  range. 

Downstream  the  slates  pass  into  a  "brecciated"  or  conglom- 
eratic layer  8  or  10  feet  thick.  This  is  followed  by  a  succession 
of  alternating,  thin  bluish  and  more  massive  grayish-buff  layers 
dipping  easterly  about  18°,  with  a  bed  of  the  grayish-buff  about 
5  feet  thick  at  the  base,  all  distinctly  sheared.  This  stratum  may 
be  repeated  for  it  is  followed  by  a  similar  series  which  is  suc- 
ceeded by  a  "brecciated"  stratum  about  30  feet  thick. 

The  rocks  which  form  the  bank  of  the  river  at  the  lower, 
western  end  of  the  gorge  were  only  casually  inspected  at  the  end 
of  a  day's  work.     No  fossils  were  found  in  them. 

Though  a  diligent  search  was  made  in  its  upper  part,  no 
fossils  other  than  those  mentioned  were  found  in  the  gorge. 

The  section  at  Highgate  Falls  shows  that  the  rocks  forming 
the  gorge  have  been  under  great  compression  and  that  some  of 
them  have  been  greatly  crushed  and  sheared.  It  is  not  clear  that 
the  "brecciation"  shown  by  the  various  rocks  is  all  of  similar 
origin.  The  fragmental  basal  portion  of  the  massive  stratum  in 
the  upper  part  of  the  northern  wall  visibly  grades  into  the  over- 
lying rock  in  such  manner  as  to  make  it  extremely  difficult  to 
imagine  just  how  it  could  be  explained  as  due  to  friction  or  mash- 
ing during  movement.  While  there  seems  to  be  some  indication 
that  the  massive  stratum  has  ridden  over  the  beds  below  it,  the 


190  REPORT  OP  THE  VERMONT'  STATE  GEOLOGIST. 

now  thoroughly  compacted  "breccia"  appears  to  be  so  related  to 
the  main  mass  of  the  massive  stratum  that  if  thrusting  did  occur 
the  "breccia"  could  readily  be  imagined  to  have  attained  its  pres- 
ent condition  prior  to  movement. 

The  evidence  of  differential  movement  between  the  massive 
stratum,  as  it  has  been  designated,  and  the  black  slates  below  it 
consists  not  so  much  in  the  identification  of  any  distinct  thrust 
plane  between  the  two  as  in  the  contrast  shown  with  respect  to 
primary  bedding  characters  and  internal  deformation.  The  crush- 
ing of  the  slates  has  been  intense.  It  seems  to  suggest  that  they 
were  crowded  by  a  heavy  mass  above  them  which  has  partly  been 
eroded.  Perhaps  they  were  also  crowded  from  beneath.  Data 
were  not  found  to  determine  whether  masses  of  very  different 
age  are  involved.  It  is  possible  that  most  of  the  rocks  belong 
to  a  conformable  or  disconformable  series  which  behaved  accord- 
ing to  the  nature  of  their  primary  structure.  The  block  of  slate 
in  which  the  fossils  were  found  has  much  the  aspect  of  an  inclu- 
sion caught  up  during  thrusting. 

Hungerford  Brook.  The  road  from  Highgate  Falls  to  St. 
Albans  crosses  Hungerford  Brook  a  mile  south  of  Highgate  vil- 
lage. At  the  bridge  and  along  and  in  the  bed  of  the  stream  east 
and  west  of  the  bridge  are  blackish  slates.  According  to  Dr. 
Howell  of  Princeton,  who  has  collected  fossils  from  these  rocks, 
but  who  wishes  to  study  his  specimens  with  care  before  an- 
nouncing his  final  conclusion,  these  slates  may  be  of  Upper  or 
late  Middle  Cambrian  age.  Dr.  Howell  bases  his  opinion  in  part 
on  the  reported  discovery  by  the  Canadian  Survey  many  years 
ago  of  Agnostus  orion  at  Hungerford  Brook.^ 

Eastern  Highgate.  The  rocks  lying  to  the  east  of  the  blue 
limestones,  slates  and  conglomerates  along  the  eastern  valley  of 
Rock  River  were  only  casually  inspected  along  the  low  ridge  near 
the  South  Gore  School  and  the  road  running  from  the  school  to 
Highgate  Center.  The  rocks  are  slates  of  very  similar  and  mon- 
otonous aspect  and  gave  no  fossils.  They  are  associated  with 
conglomerate  at  some  places.  It  would  require  further  study  to 
reach  any  tentative  opinion  of  the  age  of  these  rocks  and  their 
relations  to  the  rocks  lying  to  the  west  of  them.  Thej  were 
mapped  as  "Georgia  Slates"  by  the  Vermont  Survey. 

Swanton  Township. 

(St.  Albans  topographic  sheet.) 

General.  Swanton  township  is  bordered  by  the  lake  on  the 
west.  It  includes  Hog  Island,  an  essentially  insular  area  joined 
to  the  mainland  by  the  delta  of  the  Missisquoi  River.  The  town- 
ship is  bounded  by  Highgate  on  the  north,  by  Sheldon  and  Fair- 
field on  the  east  and  by  St.  Albans  on  the  south. 

'Personal  communication. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  Igl 

Hog  Island.  Hog  Island,  so-called,  is  the  western  extremity 
of  a  peninsula  jutting  into  Lake  Champlain.  The  designation  of 
island  is  probably  wholly  correct  with  respect  to  the  relation  of 
the  hard  rock  portion  of  the  peninsula  to  that  of  the  Vermont 
mainland ;  but  the  island  and  mainland  are  now  joined  by  modified 
delta  and  flood  plain  deposits  of  the  Missisquoi  River  which  oc- 
cupy a  strip  from  two  and  a  half  to  three  miles  wide,  extending 
from  Maquam  Bay  at  the  south  to  the  eastern  portion  of  Missis- 
quoi Bay  at  the  north.  Over  this  delta  surface  the  Missisquoi 
River  now  courses  northward,  in  which  direction  it  is  extend- 
ing its  delta  into  Missisquoi  Bay.  The  river  enters  the  bay  by 
three  short  distributaries.  Three  sluggish  water  channels,  known 
respectively  as  Dead,  Maquam  and  Charcoal  Creeks,  probably 
mark  former  distributary  outlets  of  the  river. 

The  hard  rock  is  exposed  along  shore  and  in  many  low-lying 
ledges  inland  and  apparently  all  belongs  to  the  shale  formation  of 
the  region.  The  rocks  are  everywhere  so  similar  in  lithology  and 
structural  features  to  those  of  Alburgh  and  North  Hero  that  de- 
scription would  be  largely  repetition.  Easterly  and  westerly  dip- 
ping beds  were  noted  and  both  were  observed  to  be  cut  by  east- 
erly-dipping cleavage. 

Northivest,  zuest  and  southwest  of  Swanton  village.  The 
slates  of  Hog  Island  undoubtedly  pass  under  the  delta  deposits  of 
the  Missisquoi  River  and  the  low  sand  plain  west  of  the  village  of 
Swanton.  There  are  few  if  any  outcrops  in  the  sand  plain,  but 
at  some  places  along  the  roads  the  surface  soil  contains  abundant 
chips  of  slate  showing  that  the  hard  rock  often  lies  close  to  the 
surface.  The  Missisquoi  from  Swanton  village  northward  rarely 
cuts  the  slate  above  the  surface  of  the  river,  as  may  be  readily 
seen  in  passing  along  the  road  that  closely  follows  the  southwest 
bank  of  the  stream ;  a  comsiderable  ledge  was  noted  on  the  north 
bank  of  the  stream  about  a  mile  north  of  Swanton  Falls. 

The  slate  outcrops  at  Swanton  Falls  in  the  western  part  of 
the  village.  The  rock  has  the  usual  characters  shown  by  the 
formation  in  its  outcrops  along  meridians  farther  west,  consist- 
ing of  slates  with  firmer  bands,  the  former  highly  cleaved  and 
the  latter  bent  or  broken  with  small  offsets.  The  slates  are  often 
graphitic  and  carry  graptolites,  which  have  retained  their  form 
but  have  largely  lost  their  thecal  structures.  They  seem  to  be 
G.  qiiadrifnucronatus. 

The  Missisquoi  River  makes  a  prominent  bend  to  the  south 
just  south  of  Swanton  village.  Southwest  and  south  of  this  bend 
is  a  wide  expanse  of  lowland  lying  between  the  lake  shore  and  a 
meridian  passing  just  east  of  the  village.  The  slate  formation 
probably  underlies  this  lowland  throughout  its  breadth  of  three 
and  a  half  miles  to  the  St.  Albans  line.  Away  from  the  lake  the 
slates  are  found  only  infrequently  over  the  flat,  sandy  plain ; 
but  along  the  lake  shore  they  are  exposed   from  Hotel  Cham- 


1P2  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

plain  southward.  They  are  laminated  mud  rocks  with  firmer 
bands,  marked  by  crushing  and  cleavage,  and  abundant  calcite 
veining.  The  shore  section  gives  the  same  lithological  and  struc- 
tural features  found  in  the  rocks  of  North  Hero  three  miles  to 
the  west. 

Between  Swanton  village  and  the  Missisquoi  River.  Swan- 
ton  village  is  situated  largely  on  a  sand  plain.  The  only  outcrops, 
except  those  at  Swanton  Falls,  occur  south  of  the  main  village 
between  the  road  running  from  Swanton  to  St.  Albans  and  the 
Missisquoi  River. 

The  rock  in  the  western  quarry  of  John  P.  Rich  (Swanton 
Lime  Works)  is  a  greatly  altered,  grayish- white,  often  somewhat 
marbly  limestone  and  as  exposed  in  the  face  of  the  quarry  gives 
little  evidence  of  bedding.  In  the  southwestern  part  of  the  quarry, 
as  exposed  in  the  summer  of  1921,  the  gray  limestone  was  seen 
resting  on  black,  graphitic,  Hmy  slate  which  is  strongly  sheared 
and  filled  with  small  veins  of  secondary  calcite  and  quartz.  In 
the  slate  a  considerable  hole  had  been  dug  apparently  to  see  to 
what  depth  the  slate  extended.  The  photograph  shows  the  gen- 
eral relations.  See  Plate  XXIII.  The  slate  is  exposed  over  a  small 
space  in  the  floor  of  the  quarry.  Its  presence  served  to  drive 
quarrying  operations  in  a  horizontal  direction  eastward. 

In  an  older  quarry  that  lies  to  the  southeast  the  rock  is 
similar  to  that  just  described,  but  shows  bedding  more  distinctly, 
with  easterly  dip.  The  gray  limestone  outcrops  abundantly  in  the 
fields  near  the  quarries.  It  is  everywhere  crystalline  and  barren 
of  fossils.  It  extends  eastward  to  the  bank  of  the  river,  forming 
conspicuous  ledges  at  the  highway  bridge.  Southeastward  and 
southward  the  rock  either  is  not  present  or  lies  under  the  sand 
plain  along  the  river.  The  whole  mass  of  this  limestone  south  of 
Swanton  village  as  now  exposed  is  about  two-thirds  of  a  mile  in 
extent  from  west  to  east  and  two-fifths  of  a  mile  from  north  to 
south.  It  is  now  separated  from  all  similar  rock  in  the  immediate 
vicinity  by  surface  material.  The  nearest  outcrop  northward  and 
the  only  one  noted  between  this  mass  and  similar  rock  east  of 
Highgate  Springs  is  about  a  mile  east-northeast  of  Swanton  village 
along  the  road  to  Highgate  Center.  At  this  place  emerging  from 
the  sand  plain  is  a  low  ridge  of  gray  hmestone  associated  with 
patches  of  buff-  or  chamois-colored  rock  which  are  probably 
parts  of  eroded  layers. 

The  gray  limestone  ends  rather  abruptly  west  of  Rich's 
quarry.  The  extent  to  which  it  overlaps  the  slate  westward  was 
not  determined.  It  is  probable  that  the  slate  passes  round  to 
the  south  of  the  limestone  mass  under  the  surface  covering ;_  for 
although  not  observed  in  the  immediate  neighborhood  of  the  lime- 
stone, or  along  the  river,  about  three-fourths  of  a  mile  to  the 
southeast,  slate  like  that  in  the  floor  of  Rich's  quarry  has  relation 
to  gray  limestone  quite  similar  to  that  shown  in  the  quarry.     This 


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REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  193 

outcrop  of  the  slate  carries  it  to  a  meridian  one-third  of  a  mile 
east  of  the  eastern  edge  of  the  limestone  mass  south  of  Swanton 
village,  and  about  one  mile  east  of  the  exposed  slate  at  Rich's 
quarry. 

Rocks  south  of  Szvanton  village,  bordering  the  eastern  margin 
of  the  lowland.  The  slate  at  the  last-mentioned  locality  is  per- 
haps 20  rods  east  of  the  Central  Vermont  railroad  track  and  a 
few  rods  south  of  the  road  which  after  skirting  the  southwestern 
bank  of  the  Missisquoi  passes  eastward  to  join  the  Swanton-St. 
Albans  road.  The  rock  occurs  in  a  shallow  pit  that  has  ap- 
parently been  excavated  for  road  material.  Just  east  of  the  slate, 
gray  limestone  with  some  darker  beds  near  the  base  and  irregu- 
larly distributed  yellow-weathering  beds  in  the  higher  portions 
forms  a  hill  just  east  of  the  slate.  The  slate  and  calcareous 
rocks  were  not  seen  in  actual  contact,  but  the  space  separating 
the  two  is  small  and  there  is  no  doubt  that  the  limestone  lies 
against  the  slate.  Some  of  the  limestone  carries  indistinct  fossil 
markings ;  the  rocks  dip  easterly  and  extend  eastward  to  within 
about  250  yards  of  the  Swanton-St.  Albans  road. 

It  was  not  possible  to  determine  the  horizon  of  the  slate 
either  at  Rich's  quarry  or  at  the  last-named  locality ;  but  there 
seems  little  doubt  that  it  represents  the  slate  formation  of  the 
lake  region  and  that  it  is  younger  than  the  limestones  with  which 
it  is  associated.  That  there  has  been  simple  inversion  of  rocks 
due  to  folding  and  overturning  seems  extremely  improbable,  for 
it  would  then  seem  that  other  rocks  should  intervene  between 
the  slates  and  limestones,  which  is  not  the  case.  The  reasonable 
inference  is  that  the  limestones  rest  by  thrust  overlap  on  the  slates 
in  both  cases.  The  relations  conform  to  the  regional  type  of 
dislocation. 

The  limestones  at  both  of  the  localities  just  described  are 
probably  of  Lower  Ordovician  and  possibly  of  Chazy  age.  This 
has  hardly  been  proved  by  fossils,  but  is  made  probable  by  com- 
parison with  similar  rocks  in  similar  relations  which  will  be  de- 
scribed beyond. 

About  50  rods  south-southwest  of  the  outcrops  last  described, 
west  of  the  main  line  track  of  the  Central  Vermont  R.  R.,  in  the 
angle  formed  by  it  and  the  Alburgh  branch,  is  a  low  hill  composed 
mostly  of  a  schistose  quartzite  or  quartzitic  slate,  apparently  with- 
out fossils.  Associated  with  this  quartzite  are  somewhat  isolated 
patches  of  bluish  limestone  in  uncertain  structural  relations  with 
the  quartzite.  In  its  thinly-bedded  character  and  litholog}^  the 
limestone  has  resemblance  to  certain  rocks  of  Trenton  age.  It 
appears  to  be  fossiliferous,  but  it  is  so  altered  that  nothing  distinct 
was  obtained.  Calcite  veining  is  frequent.  The  limestone  shows 
its  bedding  better  at  some  places  than  at  others  and  occasionally 
presents  a  wavy  arrangement  in  the  outcropping  edges  of  the  beds. 
It  appears  to  have  been  caught  up  by  the  quartzite.     The  distribu- 


194  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

tion  of  the  limestone  in  the  quartzite  is  pecuHar.  A  conspicuous 
exposure  occurs  just  west  of  the  track.  This  is  followed  west- 
ward by  quartzite  and  then  occurs  another  somewhat  band-like 
strip  of  the  limestone  which  seems  to  be  lar*gely  surrounded  by 
the  slaty  quartzite.  The  dip  of  both  rocks  is  easterly.  It  is  sus- 
pected that  the  quartzite  is  repeated  and  that  the  limestone  may 
also  be.  The  distribution  and  visible  structure  thus  gives  a  rough 
suggestion  of  interbedding-,  which  however  does  not  seem  prob- 
able. The  whole  width  of  this  hill  from  east  to  west  is  perhaps 
200  or  250  yards.     The  rocks  to  the  west  of  it  are  concealed. 

About  100  yards  south  of  this  hill,  and  just  west  of  the  main 
line  track  a  small  outcrop  of  the  schistose  quartzite  emerges  from 
the  surface  covering  in  the  low  ground  and  just  south  of  this  is  a 
small  exposure  of  thinly-bedded,  bluish  limestone. 

A  third  of  a  mile  to  the  south  of  these  last-mentioned  out- 
crops, just  north  of  Swanton  Junction  and  west  of  the  track,  is 
another  hill  which  shows  a  very  dififerent  kind  of  rock.  It  belongs 
to  the  quartzite-dolomite  or  Red  Sandrock  series  lying  to  the  east, 
presently  to  be  described.  On  the  east  side  of  the  hill  the  bedding 
dips  easterly  at  a  moderate  angle  for  the  most  part,  but  at  the 
northeastern  end  near  a  small  quarry,  beds  which  dip  easterly  at 
a  high  angle  lie  against  others  with  varying  westerly  dip.  This 
hill  shows  a  prominent  scarp  on  the  west,  perhaps  60  or  75  feet 
high,  with  the  beds  apparently  dipping  westerly  at  a  high  angle. 
At  the  west  the  descent  is  everywhere  abrupt  to  the  surface  of 
the  low  ground  that  lies  to  the  west.  No  contacts  with  the  rocks 
that  lie  beneath  the  plain  were  found. 

South  of  this  hill  a  private  road  runs  westward  across  the 
plain  to  two  farm  houses  about  one-half  mile  west  of  the  Junc- 
tion. The  houses  stand  on  a  low  ridge,  on  the  east  side  of  which 
is  a  considerable  thickness  of  rather  heavily-bedded  limestone, 
some  of  which  is  striped  exactly  like  many  exposures  of  the  so- 
called  Middle  Chazy  in  other  parts  of  the  lake  region.  The  beds 
of  this  series  dip  easterly  at  a  high  angle  and  have  a  sinuous 
strike  with  probable  offsets.  M.  magna  was  not  found,  but  a 
ledge  just  north  of  the  barn  gave  numerous  specimens  of  the 
characteristic  Girvanella  ocellata  (Seely).  These  rocks  are  suc- 
ceeded westward  by  beds  of  grayish-black  limestone  weathering 
to  a  lighter  gray  than  the  Chazy  and  possessing  all  the  lithological 
characters  of  the  Black  River.  They  dip  easterly  like  the  Chazy 
beds  and  are  full  of  small  calcite  veins.  Fossils  were  not  found. 
West  of  these,  also  dipping  easterly,  and  apparently  conformable 
with  the  Black  River  beds,  are  thinly-bedded,  blue  limestones  of 
probable  Trenton  age.  Crinoid  stems,  weathered  section  of  shells 
and  a  much  worn  brachiopod  were  found  with  other  indistinct 
fossils.     The  terrane  is  only  partly  represented. 

These  apparently  conformable  beds  are  thus  seen  to  be  over- 
turned, probably  on  the  western  limb  of  an  anticlinal  fold,  but  pos- 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  195 

sibly  on  the  eastern  limb  of  a  syncline.  The  rocks  in  the  plain, 
both  east  and  west  are  concealed.  The  writer's  notes  record  no 
siliceous  beds  in  the  Chazy  at  this  place.  The  Black  River  seemed 
to  be  in  conformable  contact  with  the  Middle  Chazy  limestone. 
This  is  a  common  association  farther  south  in  Vermont ;  but  it 
will. appear  from  later  discussions  that  there  are  differences  in 
the  ways  in  which  these  associated  formations  are  deformed  at 
various  places.  The  field  relations  at  this  place  did  not  suggest 
any  marked  dislocations  among  the  dift"erent  members.  As  a 
Avhole,  however,  they  are  thought  of  as  resting  by  thrust  against 
younger  rocks  at  the  west. 

A  half  mile  to  the  south-southeast  is  the  large  mass  in  which 
the  Fonda  quarry  is  excavated.  It  forms  a  hill  just  west  of  the 
railroad  track.  The  quarry  has  been  sunk  in  the  western  slope 
of  a  massive,  crystalline,  gray  limestone  which  forms  much  of  the 
higher  portion  of  the  hill.  Except  for  some  blackish  layers  at 
one  place  in  the  floor  of  the  quarry  the  rock  has  much  the  same 
appearance  throughout  and  shows  bedding  imperfectly  preserved, 
with  easterly  dip.  The  rock  is  very  much  like  that  south  of 
Swanton  village.  South  of  the  quarry  on  top  of  the  ridge  is  a 
sort  of  "hog-back"  of  altered  calcareous  sandstone  or  quartzite, 
perhaps  200  yards  long  and  50  to  75  feet  wide,  which  does  not 
appear  in  the  quarry  and  seems  to  be  surrounded  by  limestone. 
East  of  this  quartzitic  rock  is  gray  limestone  associated  with 
layers  weathering  to  a  pinkish  buff,  which  approach  close  to  the 
railroad  track.     East  of  the  track  is  the  Red  Sandrock. 

The  ridge  in  which  the  quarry  is  located  descends  westward 
by  irregular  surface  to  the  plain  that  extends  towards  the  lake. 
The  various  rocks  outcropping  on  the  intermediate  level  west  of 
the  ridge  have  a  confused  arrangement.  At  the  west  are  beds 
which  are  apparently  to  be  correlated  with  the  Chazy.  The  strike 
of  these  beds  at  some  places  changes  as  much  as  90°  within  a 
few  feet.  They  are  associated  with  rocks  having  the  markings 
of  the  Black  River  and  veined  with  white  calcite.  Numerous 
outcrops  of  thin,  blue  limestones  were  noted  in  no  very  regular 
relation  to  the  other  rocks.  The  latter  carry  obscure  fossils  and 
seem  to  be  of  Trenton  age. 

The  various  rocks  about  Eonda's  quarry  have  been  much  dis- 
turbed. They  have  probably  been  broken  by  thrusts.  All  are 
more  or  less  crystalline,  but  this  condition  is  most  apparent  in  the 
massive,  gray  limestone  and  associated  beds  forming  the  eastern 
portion  of  the  mass.  The  massive  beds  in  the  eastern  portion  of 
the  hill  have  probably  been  broken  within  themselves  and  have 
also  moved  against  the  rocks  now  forming  the  lower  western  part 
of  the  hill  and  all  of  them  are  probably  in  thrust  relations  to 
younger  rocks  lying  beneath  the  plain  at  the  west.  A  certain 
amount  of  flowage  and  crystallization  serving  to  integrate  and 
weld  layers  into  massive  rocks,  accompanied  by  a  certain  amount 


196  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

of  folding  and  fracture,  were  the  apparent  modes  of  deformation 
of  the  rocks  prior  to  a  bodily  thrust  of  all  the  rocks  to  the  west, 
over  the  slates. 

Thrusting  may  produce  an  apparent  inversion  of  strata,  but  in 
such  cases  usually  very  thick  and  massive  rocks  are  involved.  The 
rocks  in  the  eastern  portion  of  the  hill  at  Fonda's  quarry  dip 
easterly  and  pass  beneath  a  series  of  beds  with  very  similar  dip, 
but  which  are  unquestionably  much  older.  The  two  series  of 
rocks  have  the  guise  of  conformability,  but  one  may  hardly  be 
deceived  thereby.  It  is  hardly  conceivable  that  the  inversion  has 
been  produced  by  overturning  of  these  massive  formations  during 
folding.     The  older  rocks  have  their  position  by  thrust. 

It  should  not  be  understood  that  inversion  of  beds  has  never 
occurred  by  folding,  even  among  somewhat  massive  rocks ;  but 
rather  that  rupture  and  dislocation  were  more  characteristic  modes 
of  deformation  among  all  the  rocks,  on  one  scale  or  other,  in 
western  Vermont  and  largely  on  account  of  the  presence  of  very 
massive  and  exceedingly  competent  strata  among  them.  Even 
among  rocks  that  folded  the  end  result  was  often,  if  not  usually,, 
fracture  and  faulting. 

South-southwest  of  Fonda's  quarry  are  two  old,  dismantled 
quarries,  formerly  known  as  Rich's  Lime  Works.  The  rocks  at 
both  these  places  are  like  the  gray,  marbly  limestone  and  asso- 
ciated yellowish-weathering  beds  at  Fonda's.  In  the  fields  nearby 
are  ledges  of  calcareous  quartzitic  sandstone.  The  rocks  at  and 
near  these  old  quarries  form  low  ridges  or  discontinuous  out- 
crops and  suggest  that  similar  rocks  may  underlie  some  of  the 
surface  deposits  of  part  of  the  lowland  roundabout.  There  is 
nothing  especially  striking  in  the  structural  features  at  these 
localities.  The  dip  is  at  a  low  angle  to  the  east.  The  southern 
quarry  is  practically  on  the  St.  Albans  line. 

The  Red  Sandrock  series  of  dolomites,  quartsites  and  slates, 
zvith  associated  limestones,  in  S  want  on  township.  The  rocks  which 
will  be  described  under  this  heading  probably  do  not  include  all 
the  rocks  belonging  to  the  Lower  Cambrian  in  Swanton.  Some 
other  rocks  that  probably  belong  in  this  terrane,  or  to  some  other 
part  of  the  Cambrian,  will  be  mentioned  beyond. 

No  outcrops  of  the  Red  Sandrock  series  were  found  in  Swan- 
ton  north  of  the  Missisquoi  River.  The  western  margin  of  these 
rocks  at  the  north  begins  just  south  of  the  river  and  about  one- 
half  mile  east  of  the  gray  limestone  at  Swanton  bridge.  From 
this  point  the  visible  margin  then  runs  southward  for  a  short 
distance  to  the  east  of  the  Swanton- St.  Albans  road  and  then 
west  of  and  roughly  parallel  with  it  to  the  St.  Albans  line,  where 
it  bends  southwesterly  in  the  direction  of  St.  Albans  Bay._ 

By  comparison  later  with  conditions  farther  south  it  will 
appear  that  the  present  western  margin  of  these  rocks  is  probably, 
at  least  to  some  extent,  an  erosion  trace  in  the  course  of  the  re- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  197 

cession  of  this  formation  eastward  and  that  it  is  essentially  an 
escarpment  softened  by  erosion. 

In  Swanton  the  members  of  this  Sandrock  formation  are  not 
in  contact  with  the  younger  rocks  that  lie  west  of  them.  The 
nearest  approach  to  visible  contact  is  southeast  of  Fonda's  quarry 
where  the  eastern  outcrops  of  the  mass  at  Fonda's  quarry  are 
Avithin  about  100  yards  of  dolomite  beds  of  the  Sandrock  series. 
As  in  Highgate  and  other  parts  of  Vermont  the  extent  of  present 
and  former  overlap  remains  uncertain  because  a  surface  section 
does  not  expose  the  younger  rocks  beneath  the  Sandrock,  east  of 
its  present  western  margin  (see,  however,  Ferrisburg  township 
described  beyond).  North  of  Swanton  Junction  the  margin 
swings  west  of  the  railroad  track  and  the  older  rocks  lie  there  on 
a  meridian  occupied  farther  north  by  outcrops  of  the  younger 
gray  limestone.  This  relation  is,  of  course,  only  a  suggestion 
of  appreciable  overlap ;  but  at  pjaces  farther  south  definite  con- 
tact relations  support  the  idea  that  the  Cambrian  beds  moved  over 
the  younger  rocks. 

Only  the  chief  variations  among  the  members  of  the  Sand- 
rock series  may  be  noted.  The  history  of  these  rocks  with  respect 
to  the  conditions  under  which  they  were  deposited  is  a  chapter  by 
itself. 

At  Barney's  quarry  a  mile  east  of  Swanton  village  and  on 
the  western  margin  of  the  Sandrock  south  of  the  Missisquoi  River, 
the  rock  has  been  removed  for  marble.  The  marble  is  a  mottled 
red  and  white  siliceous  dolomite  of  "brecciated"  appearance. 
Similar  rock  appears  at  other  places  in  Swanton  and  in  the  town- 
ships to  the  south  and  its  various  outcrops  often  appear  to  mark 
approximately  the  same  horizon,  although  it  seems  possible  that 
its  pecuHar  features  are  repeated  in  different  beds.  Bowlders  of 
this  rock  are  common  on  the  islands  of  the  lake  and  on  the  main- 
land. So  far  as  it  may  be  distinguished  by  color  markings,  the 
mottling  is  a  variable  feature  and  in  the  same  bed  the  mottled 
rock  appears  to  pass  laterally  into  other  rock  of  more  homo- 
geneous color  and  texture.  While  in  a  great  many  of  its  outcrops 
this  mottled  rock  is  certainly  not  far  above  the  supposed  plane 
of  shear  of  the  series  of  which  it  is  a  member,  the  rock  itself  does 
not  seem  to  give  convincing  evidence  that  its  apparently  brecciated 
character  was  acquired  from  crushing  during  thrusting.  If  the 
apparent  brecciation  is  an  effect  of  internal  deformation  it  would 
seem  that  unusual  primary  conditions  must  have  existed,  such, 
perhaps,  as  an  alternation  of  thin  beds  of  sandy  and  magnesian 
deposits.  It  is  possible  to  imagine  that  such  beds  under  pressure 
could  be  broken  and  crushed  with  subsequent  welding  of  the 
whole  into  the  massive  condition  which  the  rock  now  shows.  On 
the  other  hand,  if  these  rocks  were  accumulated  in  shallow  water, 
which  seems  probable,  it  is  possible  to  imagine  that  minor  disturb- 
ances during  deposition  might  have  produced  the  confusion  and 


198  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

that  the  compacted  condition  was  effected  by  consoHdation  under 
burial,  or  by  dynamic  pressure,  or  both.  The  gray  and  red  rocks 
into  which  the  mottled  variety  seems  to  grade  many  times  do  not 
seem  to  show  appreciable  shearing  deformation. 

The  rock  yields  few  if  any  fossils.  Obscure  markings  that 
might  be  interpreted  in  different  ways  are  found  in  the  more 
homogeneous  beds  above  and  below  the  mottled  rocks.  Probably 
some  of  these  represent  filled  mud  cracks  or  other  purely  physical 
features  of  shallow  water  deposits. 

The  generally  massive,  siliceous  dolomites,  including  the  mot- 
tled marble,  pass  eastward  at  the  surface  into  rusty-weathering, 
sandy  shales  or  shaly  sandstones,  often  "flaggy."  The  latter 
outcrop  frequently  in  the  pasture  along  the  road  from  Barney's 
quarry  eastward  toward  Donaldson's  farm.  These  rocks  carry 
fragments  of  trilobites  and  in  their  lithological  features  are  much 
like  the  shales  at  "Parker's  ledge"  in  Georgia  township. 

In  the  woods  north  of  the  pasture  road  just  mentioned,  and 
perhaps  one-fifth  of  a  mile  from  it,  is  a  small  ledge  of  limestone, 
apparently  interbedded  in  the  Sandrock  formation,  from  which 
were  collected  several  specimens  of  a  fossil  identified  as  Kutorgina 
lahradorica,  var.  sivantonensis.  The  writer  was  guided  to  this 
locality  by  Mr.  Donaldson  and  Mr.  Bluett  of  Waterbury,  Conn. 
This  fossiliferous  rock  was  not  found  elsewhere  by  the  writer. 

East  of  Donaldson's  farm,  between  it  and  a  road  running 
north  and  also  east  of  the  road,  are  numerous  ledges  of  rusty- 
weathering,  sandy  shales  which  were  regarded  as  the  eastward 
extension  of  those  described  above  and  as  probably  of  Lower 
Cambrian  age. 

Except  for  the  limestone  member  the  series  as  just  described, 
from  sections  made  across  it  at  different  places,  was  observed  to 
form  a  broad  band  occupying  nearly  the  whole  width  between  the 
Swanton-St.  Albans  road  on  the  west  and  the  Highgate-St.  Albans 
road  on  the  east,  and  extending  practically  from  the  northern 
boundary  of  Swanton  township  into  St.  Albans  at  the  south.  The 
dip  is  usually  easterly  at  a  low  angle.  About  a  mile  east  of 
Donaldson's  and  about  one-fifth  of  a  mile  west  of  the  Highgate 
road  a  westerly  dip  was  noted. 

East  of  Donaldson's  the  shales  seem  to  be  more  conspicuously 
sheared  than  farther  west  and  some  of  them  are  on  meridians 
occupied  farther  south  by  ledges  of  gray  dolomite.  It  was  not 
clear  whether  shales  passed  laterally  into  dolomite ;  but  at  other 
places  yet  to  be  described,  the  field  relations  are  not  inconsistent 
with  such  a  view,  although  probable  disturbances  among  the 
rocks  must  always  be  kept  in  mind. 

The  so-called  "Intrafonnational  Conglomerate"  and  asso- 
ciated rocks  along  the  Highgate-St.  Albans  road  and  at  other  out- 
crops in  Swanton.  South  of  Hunger  ford  Brook  in  Highgate,  and 
just  north  of  the  Swanton  line,  begins  a  series  of  outcrops  of 


O  o 
+-1 

^« 

aim 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  199 

various  rocks  which  from  their  field  relations  all  seem  clearly  to 
belong  to  the  same  formation.  The  principal  exposures  are  along 
or  near  the  Highgate-St.  Albans  road  which  these  rocks  rather 
closely  follow  southward  for  a  distance  of  about  four  miles. 
Outcrops  become  more  intermittent  towards  the  south.  At  the 
south  in  Swanton,  scattered  outcrops  in  the  drift  extend  the 
geographical  range  of  these  rocks  east  of  the  Missisquoi  Branch 
of  the  C.  V.  R.  R.  to  the  base  of  the  quartzite  hills  in  the  south- 
eastern part  of  the  township,  and  apparently  show  that  this  forma- 
tion was  once  more  widely  represented  over  the  surface  than  now. 
However,  as  now  preserved,  these  rocks  form  for  the  most  part  a 
rather  narrow  belt  on  the  east  of  the  broader  band  of  quartzite, 
dolomites  and  shales  described  above. 

The  most  conspicuous  member  of  this  series  is  a  coarse  con- 
glomerate whose  fragments  vary  in  size  from  small  pieces  to 
huge  slabs  or  blocks  weighing  tons.  With  the  conglomerate  and 
forming  its  paste  or  matrix  is  a  finely-granular  (arenaceous), 
calcareous  sandstone,  which  at  some  places  forms  a  stratum  on 
which  the  conglomerate  rests,  apparently  conformably.  The 
characters  of  the  conglomerate  and  its  associated  sandstone  are 
well  shown  north  of  Skeels  Corners,  to  the  west  of  the  road.  At 
this  place  the  sandstone,  which  is  coarsely  bedded,  forms  an 
irregular  stratum  beneath  the  conglomerate  about  30  or  40  feet 
thick.  The  rock  is  prominently  siliceous  and  carries  many  small 
veins  of  quartz  which  have  weathered  out  in  relief  against  the 
body  of  the  rock.  The  accompanying  photograph  shows  the 
surface  of  the  conglomerate  at  this  locality.  See  Plate  XXIV.  The 
larger  fragments  of  the  conglomerate  are  often  large  slabs  of 
grayish  or  bluish  limestone  and  these  are  mingled  with  many 
smaller  pieces  of  all  sizes. 

In  the  conglomerate  the  matrix  is  not  always  distinct  from 
the  included  fragments  when  the  latter  are  small.  The  material 
surrounding  the  coarser  blocks  is  itself  a  conglomerate-breccia, 
showing  many  small  fragments  on  a  broken  surface. 

North  of  Skeels  Comers  the  conglomerate  and  its  associated 
rocks  continue  northward  as  a  low  ridge  west  of  the  road,  and 
by  intermittent  outcrops  along  the  road,  nearly  to  Hungerford 
Brook.  One-fourth  of  a  mile  north  of  the  Swanton  line  an  expo- 
sure on  the  west  side  of  the  road  gives  unbroken  thin  beds  of 
bluish  limestone,  perhaps  2  or  3  inches  thick,  dipping  westerly 
and  passing  upward  into  broken  and  dislocated  layers. 

East  of  the  road,  north  of  the  latitude  of  Skeels  Corners,  the 
surface  west  and  east  of  Hungerford  Brook  is  flat,  with  the  hard 
rock  mostly  concealed.  Along  the  road  by  Webster  School  are 
low-lying  ledges  of  slate  like  that  in  eastern  Highgate,  to  the  east 
of  Rock  River.  So  far  as  surveyed  over  this  fiat  land  east  of 
Skeels  Corners,  no  conglomerate  or  limestone  was  observed. 


200  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

South  of  Skeels  Corners,  along  the  road  or  in  the  fields,  the 
members  of  this  conglomerate-limestone  formation  outcrop  at  in- 
tervals to  within  a  mile  of  the  St.  Albans  line.  To  the  east  the 
hard  rock  that  outcrops  here  and  there  through  the  extensive 
surface  material  is  largely  slate;  but  south  of  the  road  to  Greens 
Corners  in  a  pasture  and  on  the  bank  of  Hungerford  Brook  is  a 
ledge  of  calcareous  rock  that  probably  is  a  part  of  the  formation 
to  which  the  conglomerate  belongs,  and  a  mile  and  a  fourth  south- 
west of  Greens  Corners,  one-third  of  a  mile  east  of  the  railroad 
track  are  inconspicuous  ledges  of  bluish  limestones  like  those 
seen  along  the  Highgate-St.  Albans  road  and  farther  north. 

Various  fossils  have  been  reported  from  this  conglomerate 
formation  at  its  outcrops  in  Swanton,  and  those  occuring  in  St. 
Albans  which  wall  be  mentioned  later,  and  these  have  been  thought 
to  indicate  a  Middle  Cambrian  age ;  but  much  uncertainty  exists 
as  to  what  forms  should  be  referred  to  the  matrix  and  what  to 
the  fragments.  In  Swanton  the  beds  near  Skeels  Corners  yielded 
a  few  fragments  of  linguloid  brachiopod  shells  whose  characters 
are  too  obscure  for  precise  determination.  In  size  and  shape  they 
resemble  as  closely  as  any  illustrated  forms,  Lingula  ric'miformis 
Hall,  or  Glossina  trentonensis  Conrad;  but  it  would  be  going 
altogether  too  far  to  claim  that  they  are  referable  to  either  of 
these  species.  It  was  not  clear  whether  the  fossils  were  in  the 
matrix  or  not. 

Southeastern  part  of  Sivanton  tozvnship.  In  the  southeast- 
ern part  of  the  township  and  in  adjoining  parts  of  Fairfield  the 
surface  rises,  forming  hilly  land.  As  inspected  near  the  track 
of  the  Missisquoi  branch  and  along  the  road  running  parallel 
with  it  on  the  southeast  the  rocks  at  the  base  of  this  high 
land  consist  of  quartzites  and  dolomites  much  like  those  found 
along  the  base  of  the  Green  Mountains  farther  south  in  Vermont 
and  are  tentatively  regarded  as  of  Lower  Cambrian  age.  The 
slates  which  underlie  the  flat  land  west  of  these  hills,  between 
them  and  Hungerford  Brook,  may  be  and  probably  are  of  Cam- 
brian age,  but  their  exact  horizon  is  not  known. 

St«  Albans  Township. 

(St.  Albans  topographic  sheet.) 

Location.     St.  Albans  township  lies  just  south  of  Swanton. 

The  lake  region.  The  broad  area  of  low,  flat  land  which 
forms  the  western  portion  of  the  township  of  Swanton  continues 
with  practically  undiminished  breadth  into  St.  Albans.  In  St. 
Albans  as  in  Swanton  the  rock  of  this  lowland  belongs  chiefly  to 
the  Ordovician  shale  formation  of  the  region.  The  shore  of  the 
lake  gives  an  almost  continuous  section  in  these  rocks  which  have 
the  same  general  characters  which  have  been  described  for  them 
on  previous  pages. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  201 

Away  from  shore  the  hard  rocks  are  mostly  concealed,  but 
outcrops  are  found  on  knolls  and  low  ridges  along-  the  roads  and 
in  the  fields.  Along  the  road  from  the  lake  shore  to  St.  Albans, 
past  School  No.  10  and  the  Tuller  School,  the  slates  were  traced 
by  scattered  ledges  eastward  to  within  one-third  of  a  mile  of 
Stephens  Brook.  A  half  mile  west  of  School  No.  10  some  riisty, 
sandy  shales  yielded  large  numbers  of  graptolites,  which  were 
identified  as  probably  Diplograptus  foliaceous,  var. 

In  its  southern  portion  the  lowland  forms  a  peninsula  known 
as  St.  Albans  Point,  which  is  separated  from  the  mainland  by 
St.  Albans  Bay. 

Among  the  shales,  or  slates  as  they  might  fittingly  be  called  in 
most  cases,  which  probably  make  up  most  of  the  lowland,  there 
occur  at  several  places  other  rocks  which  are  very  doubtfully 
members  of  the  shale  formation.  In  spite  of  somewhat  scanty 
representation  at  the  present  time,  these  rocks  may  possibly  have 
some  structural  significance. 

In  the  first  place  these  rocks  may  be  described  as  appearing 
to  have  a  stranded  position  among  the  shales  and  as  foreign  to 
them.  They  have  not  been  seen  elsewhere  in  the  region  in  such 
relations  nor  in  any  other  relations  to  the  shales.  In  all  their 
outcrops  these  rocks  now  form  dense,  very  much  altered  quartz- 
ites,  weathering  white,  but  on  fresh  surfaces  appearing  blackened 
as  though  at  one  time  they  had  been  in  a  very  hot  fire.  They  are 
extremely  tough  and  break  reluctantly  under  the  hammer.  Be- 
cause of  the  way  in  which  they  weather,  their  outcrops  are  con- 
spicuous when  close  at  hand,  although  they  do  not  form  large  ex- 
posures nor  high  elevations.  In  the  course  of  a  general  survey  of 
the  lowland  along  the  roads  and  in  adjacent  fields  the  outcrops  of 
these  rocks  were  sufficiently  conspicuous  and  different  from  the 
shales  to  call  for  a  special  examination.  With  the  possibility 
always  in  mind  that  on  the  islands  of  the  lake  or  over  the  lowland 
bordering  its  shore  there  might  somewhere  be  found  some  rem- 
nants of  overthrust  rocks  that  once  lay  on  the  shales  but  which 
have  now  largely  disappeared  by  erosion,  these  rocks  were  at  first 
hailed  as  possibly  affording  an  example  of  what  had  so  persistently 
been  sought.  Since  their  outcrops  are  all  low  and  topographically 
merge  with  the  surrounding  slates,  it  is  possible  that  they  are  more 
extensive  than  is  apparent  and  possibly  there  are  other  visible 
ledges  which  were  not  seen. 

The  possible  significance  of  these  rocks  seems  to  lie  partly  in 
their  geographical  situation  and  relations  and  partly  in  the  fact 
that  they  have  not  been  seen  at  any  place  as  forming  a  part  of 
the  shale  formation. 

The  northernmost  outcrops  which  were  seen  lie  between  the 
lake  shore  and  Jewett  Brook,  about  a  mile  and  a  half  north-north- 
west of  the  Point  School.  At  this  place  the  rock  has  the  greatest 
surface  extent  of  any  of  the  exposures  seen.     It  forms  three  low 


202  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

knolls  in  a  north-south  line  and  smaller  patches  west  of  them. 
Roundabout  are  ledges  of  other  rock  more  like  the  shale-slate 
formation,  but  not  always  of  well-defined  character.  Typical 
shale,  however,  outcrops  to  the  north  on  a  meridian  slightly  to 
the  east,  and  also  westward. 

A  mile  south-southwest  on  the  road  running  from  the  lake 
shore  to  St.  Albans  Bay  and  one  mile  northwest  of  the  Point 
School  are  other  outcrops,  along  and  near  the  road.  In  a  low 
ridge  just  east  of  the  road  the  bedding  is  distinct  and  there  is  a 
small  fold  overturned  to  the  west. 

Other  outcrops  occur  practically  on  the  same  meridian  with 
the  last  mentioned  in  the  southern  portion  of  St.  Albans  Point. 
About  two-thirds  of  a  mile  north  of  Hathaway  Point,  at  the 
summer  place  of  Mr.  Morton  of  St.  Albans,  shales  may  be  seen 
to  form  a  high  cliff  along  shore.  Above  the  bank  in  the  yard 
near  the  highway  occurs  a  small  exposure  of  dense,  white- 
weathering  quartzite  which  appears  to  be  in  place.  At  the  ex- 
tremity of  Hathaway  Point  the  quartzitic  rock  appears  to  lie  on 
greatly  sheared  and  disturbed  slate  and  the  two  are  much  involved. 
The  relations  strongly  suggest  a  thrust  contact.  Along  the  road 
from  Hathaway  Point  to  "Kamp  Kill-Kare"  and  in  the  fields 
west  of  this  road  are  other  outcrops  of  the  quartzite,  which  west- 
ward gives  place  to  typical  shale. 

The  quartzite  gives  little  or  no  hint  as  to  its  age.  It  lies  on 
meridians  which  farther  south  on  the  mainland  in  Georgia  town- 
ship, south  of  St.  Albans,  are  occupied  by  shales  and  overthrust 
limestones  and  members  of  the  Red  Sandrock  series.  It  seemed 
to  the  writer  not  unlikely  that  the  small  areas  of  quartzite  just 
described  may  be  residuary  fragments  of  a  formerly  much  more 
extensive  mass  of  such  rocks,  or  of  others  structurally  related  tO' 
them,  which  once  lay  on  the  slates.  The  imagination  must  be 
exercised  in  such  a  view,  but  the  suggestion  is  not  without  sup- 
port from  other  field  relations  in  nearby  areas.  East  of  Stephens 
Brook,  north  of  the  village  of  St.  Albans  Bay,  are  physiographic 
outliers  of  altered  limestones,  presently  to  be  discussed,  which 
are  now  nearly  a  mile  removed  from  the  erosion  margin  of  similar 
rocks  which  outcrop  from  beneath  the  massive  quartzites  and 
dolomites  of  the  Lower  Cambrian  Red  Sandrock  series.  These 
limestone  masses  are  quite  clearly  eroded  thrust-inliers  in  the 
shale  formation. 

Equal  in  interest  to  the  evidence  of  remarkable  thrust  phe- 
nomena which  the  region  shows  are  the  indications  of  the  great 
amount  of  erosion  which  apparently  must  have  occurred  in  pro- 
ducing the  present  relations  among  the  rocks. 

Limestones  east  of  Stephens  Brook  in  St.  Albans.  Leaving 
the  main  road  that  connects  the  village  of  St.  Albans  Bay  and 
the  city  of  St.  Albans,  about  two-thirds  of  a  mile  from  the  lake 
shore,  is  a  road  running  northward  towards  the  Tuller  School. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  203 

Along  its  southern  portion  this  road  is  bordered  on  both  sides  by 
marbly  gray  or  dove-colored  limestone,  but  northward  this  rock 
occurs  mostly  on  the  east  side  of  the  road  where  it  forms  the 
lower  portion  of  a  scarp-slope  that  is  capped  by  the  Red  Sand- 
rock.  About  a  mile  north  of  the  St.  Albans  road,  west  of  the  one 
running  northward,  are  low  outcrops  of  bluish  limestone  which 
may  be  of  Trenton  age.  The  gray  limestone  is  intermingled  with 
some  sandstone  and  carries  yellow-weathering  layers.  Without 
much  doubt  these  rocks  are  the  same  as  those  at  Rich's  old 
quarry  and  at  Fonda's  quarry  farther  north.  With  some  inter- 
ruptions these  rocks  continue  northward  to  within  about  a  mile 
of  the  Tuller  School.     The  dip  is  prevailingly  to  the  east. 

North  of  the  village  of  St.  Albans  Bay  and  three-fourths  of 
a  mile  west  of  the  road  just  described  as  running  northward,  are 
two  hills  composed  of  gray  limestone  which  has  in  its  striped 
appearance  at  places  much  resemblance  to  certain  rocks  which 
the  writer  has  elsewhere  identified  with  the  Chazy.  The  rock  is 
altered  and  massive  in  general  appearance,  with  obscure  dip  and 
strike.  Faint  markings  were  noted,  but  no  distinct  fossils  were 
found.  These  two  hills  are  probably  joined  beneath  the  surface 
material,  but  taken  together  they  are  isolated  from  the  rocks 
forming  the  scarp  to  the  east  and  are  probably  surrounded  by 
slates.  The  slates  are  largely  concealed  roundabout,  but  outcrop 
to  the  west  of  the  larger  western  hill. 

In  and  south  of  St.  Albans  Bay  village.  East  of  the  village 
of  St.  Albans  Bay  the  escarpment  formed  by  the  gray  limestone, 
with  its  associated  rocks  and  the  Red  Sandrock  formation  and 
which  in  general  borders  the  lowland  on  the  east,  is  broken  by  an 
embayment  along  which  ascends  the  road  from  St.  Albans  Bay  to 
the  city.  This  embayment  marks  a  surface  interruption  in  the 
band  of  limestone  and  an  eastward  curve  in  the  margin  of  the 
Red  Sandrock.  South  of  the  road  the  margin  of  the  Cambrian 
rocks  swings  westward  and  in  the  eastern  part  of  the  village  of 
St.  Albans  Bay  the  Sandrock  is  again  in  proximity  to  the  gray 
limestone  south  of  the  brook.  To  the  west  of  the  dove-gray 
limestone  occur  other  limestones  which  are  much  sheared  and 
altered.  Some  of  it  appears  like  the  dense,  black  limestone  found 
with  the  Trenton  at  Highgate  Springs  and  possibly  represents 
the  Black  River.  Southwest  of  the  Catholic  church  and  in  other 
outcrops  nearby  are  ledges  of  bluish  limestone,  weathering  gray, 
which  are  sheared  and  veined  with  calcite.  This  rock  shows 
fragments  of  fossils  on  the  weathered  surface  and  a  small  bowlder 
gave  a  worn  brachiopod  shell  like  Strophomena.  The  rock  is 
probably  Trenton  and  resembles  other  rock  correlated  with  Tren- 
ton at  localities  to  the  north. 

South  of  the  village,  to  the  east  of  the  shore  road,  is  gray 
limestone  with  some  chamois-colored  rock,  associated  with  dense, 
blackish  limestone  carrying  demilunar  traces  of  fossils  which  are 


204  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

like  the  markings  which  so  frequently  occur  in  the  Black  River. 
Bluish,  so-called  Trenton  limestone,  is  scantily  represented.  All 
the  rocks  are  sheared  and  veined  with  calcite.  West  of  the  shore 
road  the  grass  land  is  flattish,  with  no  outcrops.  The  shale 
formation  probably  underlies  the  surface  material  near  the  lake 
shore. 

The  Red  Sandrock  series  in  St.  Albans  tozvnship.  The 
Lower  Cambrian  quartzite-dolomite  series  of  Swanton  continues 
southward  across  the  St.  Albans  line.  Along  their  western 
margin  the  Cambrian  rocks  cap  the  gray  limestones  as  described 
above  and  may  be  seen  in  actual  contact  at  two  places,  at  least. 
With  the  limestone  the  Cambrian  rocks  form  an  escarpment 
which  faces  the  lowland  and  lake  to  the  west.  In  St.  Albans  the 
Cambrian  massive  dolomites  and  quartzites  are  most  prominently 
exposed  along  a  ridge  about  one  mile  wide  just  east  of  the  escarp- 
ment. A  section  made  across  the  strike  due  west  of  St.  Albans 
city  showed  essentially  the  same  sequence  of  massive  reddish, 
gray  and  mottled  rocks  as  found  in  the  western  portion  of  the 
band  of  Cambrian  rocks  as  described  for  Swanton.  A  reading 
on  a  bed  of  the  mottled  "Swanton  marble"  gave  the  strike  as 
N.  10°  E.  and  the  dip  as  8°  easterly.  The  sequence  is  practically 
duplicated  at  the  Georgia  line  with  approximately  the  same  dip 
and  strike. 

East  of  the  ridge,  along  the  valleys  of  Stephens  and  Rugg 
Brooks,  respectively  northwest  and  southwest  of  St.  Albans  city, 
the  surface  is  lower  and  the  rocks  are  extensively  covered ;  but 
apparently  Lower  Cambrian  rocks  underlie  most  of  the  surface 
in  the  area  between  the  western  marginal  scarp  and  the  main  road 
that  runs  from  Georgia  through  St.  Albans  city  to  Highgate.  In 
the  western  outskirts  of  the  city  of  St.  Albans,  north  of  the  road 
to  St.  Albans  Bay,  scattered  ledges  of  sheared  quartzite  outcrop 
only  short  distances  from  small  ledges  of  conglomerate  and  slate 
which  will  be  mentioned  again  beyond,  and  well-bedded  quartzite. 
not  notably  sheared,  forms  low  but  prominent  ledges  on  and  near 
the  main  road  from  St.  Albans  city  to  Georgia,  about  a  mile  south 
of  the  center  of  the  city. 

Aldis  Hill.  Aldis  Hill,  to  the  northeast  of  the  city,  is  ap- 
parently composed  chiefly  of  gray  quartzite.  At  the  northern  end 
of  the  hill  the  beds  may  be  plainly  seen  dipping  at  a  moderate 
angle  in  a  direction  a  little  to  the  north  of  west.  On  the  north- 
east slope  of  the  hill  the  edges  of  the  beds  are  well  exposed  and 
many  of  them  may  be  seen  to  be  only  from  2  to  3  inches  thick. 
They  carry  frequent  thin  veins  of  quartz  and  are  somewhat  but 
not  severelv  sheared. 

St.  Albans  Hill.  This  hill  lies  partly  in  St.  Albans  and  partly 
in  Georgia  township.  It  is  a  prominent  eminence  lying  just  east 
of  the  St.  Albans-Georgia  road. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  205 

A  private  road  leaves  the  main  road  about  two  miles  south 
of  the  center  of  the  city,  and  passes  round  the  northwestern  end 
of  the  hill.  Along  and  near  this  road,  perhaps  30  or  40  rods 
west  of  the  main  road,  are  low-lying  ledges  of  blue  limestone 
carrying  some  conglomerate.  The  topography  suggests  that  there 
is  a  fault  at  the  northern  end  of  the  hill  and  that  this  limestone  is 
on  the  downthrow  side.  On  the  supposedly  upthrow  side  is 
massive  quartzite.  This  apparent  displacement  is  seemingly  trace- 
able in  a  southeast  direction  on  the  east  side  of  the  hill,  passing  to 
the  west  of  the  farm  house.  Over  the  hill  to  the  west  and  south 
the  rocks  are  quartzite,  sheared  quartzite  or  phyllite,  and  dolomite, 
in  such  arrangement  as  to  suggest  that  possibly  that  there  was 
lateral  variation  in  the  different  beds  and  that  some  of  the  rocks 
were  sheared  more  than  others ;  also  that  there  may  have  been 
some  faulting  and  offsetting  so  as  to  bring  different  rocks  along 
the  same  line  of  strike.  The  western  slopes  are  generally  steep. 
On  the  southwestern  side  (in  Georgia)  are  precipitous  scarps 
which  mark  dislocations. 

Southeastern  part  of  St.  Albans  toivnship  and  adjoining  parts 
of  Fairfield  and  Fairfax.  East  of  St.  Albans  Hill  the  boundaries 
of  the  townships  of  St.  Albans,  Fairfield  and  Fairfax  meet  at  a 
common  point.  East  of  this  point,  at  the  southwestern  end  of 
Bellevue  Hill,  are  interbedded  quartzite,  dolomite  and  mottled 
rocks  practically  on  end,  dipping  at  a  high  angle  to  the  west  or 
east.  At  the  base  of  the  series  is  a  stratum  of  dolomite  which 
looks  as  though  it  had  been  crushed.  It  breaks  into  fragments 
which  usually  have  small  unaltered  cores  surrounded  by  rusty, 
decomposed  rock.  These  various  rocks  lie  about  a  mile  east  of 
St.  Albans  Hill.  They  are  regarded  as  forming  the  eastward 
continuation  of  the  rocks  of  the  hill,  or  a's  possibly  lying  strati- 
graphically  just  below  them ;  but  in  either  case  as  members  of  the 
Lower  Cambrian  series.  North  of  these  rocks  quartzite  forms 
the  western  base  of  Bellevue  Hill. 

Bellevue  Hill.  The  rocks  on  the  northwestern  slope  of  Belle- 
vue Hill  vary  somewhat  in  character  and  are  prevailingly  sheared 
into  foliated  rocks.  Apparently  depending  upon  their  original 
texture  they  are  now  sometimes  phyllitic,  sometimes  schistose  or 
gneissoid.  In  one  place  a  conglomerate  was  noted,  sheared  into 
a  coarse  gneiss  in  which  the  squeezed  pebbles  could  be  plainly 
seen.  Distinct  small  folds  may  be  observed  in  some  places,  par- 
ticularly on  weathered  joint  planes  cutting  across  the  strike.  The 
prevailingly  easterly  dip,  as  viewed  on  the  surface,  is  then  seen 
to  be  that  of  an  induced  structure.  The  colors  are  greenish,  gray 
and  sometimes  purplish.  The  rocks  are  all  prominently  siliceous 
in  composition  and  in  general  strongly  suggest  the  basal  portion, 
of  some  overlapping  formation.  Well-defined  bedding,  repeated, 
small,  sometimes  overturned  folds,  variations  in  the  purity  of  the 
material  and  in  the  texture,  all  seem  to  accord  best  with  the  idea 


206  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

that  these  rocks  are  later  than  pre-Cambrian.  They  are  possibly 
altered  derivatives  of  older  rocks,  not  now  exposed,  and  have 
been  sheared  into  schists  and  gneisses  whose  surface  exposures 
are  deceptive. 

The  topography  suggests  that  Bellevue  Hill  is  part  of  an  up- 
thrust  mass  of  rocks.  The  western  slope  is  steep  and  is  really  a' 
softened  scarp.  A  banking  of  bowlder  drift  and  a  heavy  cover- 
ing of  trees  conceals  the  really  precipitous  character  which  the 
slope  now  has  at  some  places.  In  the  recognition  of  the  upthrust 
relation  of  this  hilly  land  at  the  east  one  finds  the  clue  to  the 
clearly  disturbed  condition  of  the  rocks  described  for  the  south- 
western end  of  Bellevue  Hill  and  for  the  westerly  dip  at  Aldis 
Hill.  The  beds  were  folded  and  sometimes  tilted  to  a  high  angle 
or  overturned  before  rupture  occurred.  Over  the  higher  por- 
tions of  the  hilly  land  the  dolomites  have  disappeared  by  erosion. 
East  of  the  supposed  plane  of  thrust  the  rocks  have  usually  been 
strongly  sheared. 

East  of  St.  Albans  city.  East  of  the  city  a  road  leads  east- 
ward over  the  rugged,  hilly  land  to  the  French  School.  The 
rocks  along  this  road  were  carefully  inspected.  As  exposed  at 
the  surface  they  vary  from  slaty  phyllites  through  coarser,  darker 
colored  schistose  or  gneissoid  quartzites  to  gray,  granular  quartz- 
ites  in  no  regular  order.  Slaty  phyllites  are  more  abundant  east- 
ward. 

The  limestone  conglomerate  and  associated  rocks  in  St.  Al- 
bans. Mention  has  already  been  made  of  the  small  outcrops  'at 
the  northern  end  of  St.  Albans  Hill  and  in  the  western  outskirts 
of  the  city.  The  latter  locality,  commonly  known  as  "Adam's 
pasture,"  is  one  that  has  been  visited  by  many  geologists  in  their 
studies  of  the  stratigraphy  of  the  region.  Logan  was  one  of  the 
first  to  report  upon  the  rocks  at  this  place  (Geology  of  Canada, 
p.  858)  and  described  them  as  part  of  a  band  that  was  traceable 
for  about  one-fourth  of  a  mile  north  of  the  road  before  it  disap- 
peared. Logan  also  described  another  band  of  conglomerate 
about  one-fourth  of  a  mile  to  the  west  at  the  base  of  a  mass  of 
whitish  sandstone.  Both  conglomerates  were  described  as  carry- 
ing fragments  of  pure  gray  limestone.  Immediately  beneath  the 
base  of  the  western  strip  "occurs  a  band  of  dark  gray,  slightly 
micaceous  slate,  with  Obolella  cingulata." 

The  writer's  observations  at  Adam's  pasture  showed  that 
what  is  present  of  this  conglomerate  formation  is  partly  sur- 
rounded by  not  very  distant  outcrops  of  sheared  quartzite,  and 
afforded  nothing  definite  as  to  the  primary  or  secondary  struc- 
tural relations  of  the  various  rocks. 

In  the  conglomerate  the  fragments  of  gray  limestone  are 
imbedded  in  a  matrix  of  calcareo-siliceous  material  like  that  found 
in  the  conglomerates  of  Swanton  and  Highgate. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  207 

West  of  the  Central  Vermont  R.  R.  track,  a  half  mile  north 
of  the  Georgia  line,  is  another  prominent  exposure  of  the  conglom- 
erate formation,  perhaps  two  acres  in  extent.  With  unimpor- 
tant variations  the  rocks  are  like  those  at  Skeels  Corners.  The 
conglomeratic  portion  shows  large  and  small  fragments  of  bluish 
or  grayish  limestones,  with  some  sheared,  marbly  limestone,  in  a 
calcareo-siliceous  matrix  which  weathers  to  a  yellowish  gray.  In 
association  with  the  conglomerate  are  distinctly  bedded  ledges  of 
arenaceous  rock  much  like  the  conglomerate  matrix.  At  this 
locality  none  of  the  thinly-bedded,  bluish  limestone  was  seen,  but 
at  the  northern  end  of  the  exposure  is  a  substantial  thickness  of 
blackish  slates  which  seem  to  lie  beneath  the  conglomerate  and 
which  have  some  resemblance  to  those  found  in  association  with 
the  blue  limestone  at  Highgate  Center.  The  formation  including 
the  conglomerate,  of  which  outcrops  at  various  places  in  High- 
gate,  Swanton  and  St.  Albans  have  now  been  described,  has 
yielded  fossils  to  various  investigators,  but  its  age  has  not  been 
completely  determined  nor  its  relations  positively  elucidated  from 
such  fossils  as  have  been  found.  From  its  apparent  relations  to 
other  Cambrian  rocks  and  from  such  fossils  as  have  been  dis- 
covered the  formation  has  been  called  Middle  Cambrian.  Dr. 
Walcott  thought  that  the  fossils  collected  by  himself  and  by  G.  E. 
Edson  indicated  such  an  age.  He  listed  thirteen  species  as  found 
in  the  various  members  of  this  formation,  among  which  Para- 
doxides,  which  was  reported  from  the  "argillite,"  seemed  to  argue 
very  strongly  for  a  Middle  Cambrian  age  for  the  formation. 

The  distribution  and  characters  of  the  various  rocks  which 
seemingly  are  to  be  regarded  as  together  making  up  this  singular 
formation  may  be  susceptible  of  another  interpretation,  in  spite 
of  the  apparent  nature  of  the  fossils.  There  is  little  doubt  from 
what  observation  the  writer  has  made  that  the  removal  of  the 
surface  covering  would  disclose  a  wider  extent  of  these  various 
rocks  than  their  present  outcrops  show. 

Georg-ia  Township. 

(St.  Albans  and  Milton  topographic  sheets.) 

Location.  This  township  which  lies  just  south  of  St.  Albans 
is  also  bordered  on  the  west  by  the  lake.  It  is  bounded  by  Fair- 
fax on  the  east  and  by  Milton  on  the  south. 

The  slates  and  gray  limestone  along  and  near  the  lake  shore 
in  Georgia.  The  gray  limestone  and  associated  rocks  found  lying 
to  the  west  of  the  margin  of  the  Lower  Cambrian  Red  Sandrock 
series  in  St.  Albans  continue  southward  into  Georgia,  forming  in- 
termittent exposures  between  the  lake  shore  and  the  margin  of 
the .  Red  Sandrock  series.  The  limestone  seldom  reaches  the 
shore,  but  is  separated  from  it  by  the  slate  formation  with  which 
it  is  in  intimate  field  association  at  several  places.     The  outcrops 


208  REPORT  OF  THE  VERMONT   STATE  GEOLOGIST. 

of  the  gray  limestone  and  its  companion  rocks  in  Georgia  may  be 
briefly  described. 

East  of  the  shore  road  running  south  from  St.  Albans  Bay 
village,  and  a  half  mile  south  of  the  St.  Albans  line,  on  "Shore 
Acres  farm,"  the  gray  limestone  with  interbedded,  yellow- 
weathering  layers,  in  some  places  may  be  seen  dipping  easterly  at 
a  high  angle.  The  rock  is.  however,  generally  much  sheared  with 
partial  obliteration  of  the  bedding.  The  gray  rock  is  associated 
at  this  locality  with  beds  carrying  markings  that  indicate  a  Black 
River  age.  The  structural  relations  are  obscure.  Above  the  lime- 
stone to  the  east  are  the  Lower  Cambrian  gray  and  mottled  dolo- 
mites dipping  easterly  at  a  low  angle. 

Just  west  of  the  shore  road,  south  of  "Shore  Acres  farm" 
and  between  it  and  Mill  River,  are  outcrops  of  sandstone  with  the 
beds  dipping  easterly  at  a  high  angle.  Just  west  of  the  sandstone 
is  bluish  limestone  which  looks  very  much  like  the  Trenton.  The 
dip  is  again  easterly  at  a  high  angle  and  the  sandstone  and  lime- 
stone appear  as  though  interbedded. 

South  of  these  outcrops  is  Mill  River.  In  the  bed  and  along 
the  sides  of  the  river,  above  and  below  the  bridge,  is  exposed  a 
gray  sometimes  obscurely  striped  limestone.  Above  the  bridge 
the  dip  is  not  clear,  but  below  it  the  bedding  may  be  seen  to  dip 
easterly  at  a  high  angle,  measured  at  one  place  as  53°. 

About  200  paces  west  of  the  bridge  the  gray  rock  is  succeeded 
westward  by  apparently  conformable  sandstone  and  shaly  lime- 
stone which  continue  west  for  about  60  paces  and  are  then  fol- 
lowed by  shaly  limestones  and  shales.  In  the  river  section  no 
beds  were  noted  which  had  any  resemblance  to  Black  River  rocks. 

Gray  limestone  outcrops  in  the  angle  of  the  roads  just  south 
of  the  Everett  School  and  one- fourth  of  a  mile  farther  south  on 
the  east  and  west  sides  of  the  shore  road.  At  Lime  Rock  Point 
the  gray  limestone  reaches  the  water's  edge,  while  south  of  the 
point  the  bank  of  the  lake  is  formed  of  slate  like  that  of  the 
St.  Albans  lowland  and  the  islands  lying  to  the  west,  but  inde- 
scribably crushed  and  jammed  so  that  its  included  firmer  bands 
of  rusty,  siliceous  rock  are  squeezed  and  faulted  out  almost  to 
obliteration. 

East  of  the  road  on  the  farm  of  Mr.  Wilcox  the  gray  lime- 
stone is  clearly  much  disturbed  and  greatly  sheared.  Just  south 
of  Wilcox's  house  black  slate  outcrops  in  the  road  and  a  fourth 
of  a  mile  farther  south  the  shale-slate  formation  may  again  be 
seen  forming  the  shore  clifif  where  the  road  closely  hugs  the  shore 
just  north  of  Melville  Landing. 

The  slate  forms  the  shore  from  the  small  point  south  of 
Melville  Landing  to  the  Milton  line.  Throughout  this  distance 
the  margin  of  the  Red  Sandrock  series  is  one-fifth  a  mile  or  less 
from  the  lake  shore.     The  Cambrian  rocks  form  the  summit  of  a 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  209 

sharp  slope  against  which  is  usually  piled  a  large  amount  of  drift. 
Through  this  covering  the  hard  rocks  outcrop  at  intervals. 

South  of  Melville  Landing  near  the  top  of  the  slope  lie  great 
blocks  spread  about  "like  ruins."  Some  of  these  are  quartzite 
and  others  are  composed  of  bluish-gray  and  chamois-colored 
limestone  with  a  "brecciated"  texture  not  unlike  that  of  the  mot- 
tled Swanton  marble.  Southward  along  the  intermediate  levels 
of  the  slope  at  several  places  the  soil  indicates  that  the  slate 
formation  is  close  to  the  surface  and  at  one  place  about  two  miles 
south  of  Melville  Landing  the  black  slate  was  found  outcropping 
Avell  up  the  slope.  A  half  mile  farther  south  the  gray  limestone 
with  abundant  calcite  veins  appears  from  beneath  the  Cambrian 
dolomites  and  forms  a  conspicuous  hill  at  the  western  base  of 
which  the  black  slate  outcrops. 

About  two  and  a  half  miles  north  of  Camp  Rich  the  shore 
road  turns  abruptly  eastward  away  from  the  bank  of  the  lake 
which  it  closely  follows  to  this  turn.  Slate  outcrops  where  the  road 
turns  again  southward.  East  and  south  of  this  slate  outcrop  is 
gray,  often  sparry  limestone  of  uncertain  correlation.  One-half 
mile  farther  south,  east  of  the  road,  sparry  limestone  has  about 
the  same  dip  as  the  Cambrian  dolomite  that  clearly  lies  above  and 
on  it.  West  of  the  road  is  other  limestone  which  continues  nearly 
to  the  slate  along  shore. 

As  indicated  above,  the  lake  is  formed  of  the  shale-slate 
from  the  St.  Albans  to  the  Milton  line,  except  at  the  Lime  Rock 
Point.  It  thus  appears  that  along  the  Georgia  shore  the  same 
general  relations  prevail  among  the  slates,  gray  limestones  and 
Cambrian  dolomites  as  in  Highgate,  Swanton  and  St.  Albans. 
In  Georgia  it  seems  probable  that  at  some  places  the  Cambrian 
rocks  rest  directly  upon  the  slates,  as  will  be  conclusively  shown 
to  be  the  case  farther  south,  and  as  may  be  the  case  at  certain 
places  north  of  Georgia ;  but  in  Georgia  and  places  north  of  it 
the  surface  covering  leaves  some  doubt. 

There  can  be  no  doubt,  however,  that  the  relations  among 
the  rocks  along  the  lake  shore  in  Georgia  clearly  mark  thrusting 
and  dislocations  and  show  that  older  rocks  have  moved  over 
younger  ones.  There  was  probably  involved  at  least  one  great 
low-angle  thrust  by  which  the  Cambrian  rocks  were  moved  to 
the  Avest.  Whether  the  gray  limestone  and  its  companion  rocks 
were  secondarily  involved  in  the  thrust  that  drove  the  Cambrian 
westward  and  were  carried  along  with  the  latter,  or  whether  they 
are  rocks  that  were  independently  driven  on  the  slates  on  which 
they  now  rest  and  were  overridden  by  a  later  major  thrust  of  the 
Cambrian  it  is  not  possible  to  tell.     Either  history  seems  possible. 

The  escarpment  formed  by  the  margin  of  the  Lower  Cam- 
brian Red  Sandrock  and  the  various  limestones  that  lie  beneath  it 
in  southwestern  Georgia  is  over  a  mile  to  the  west  of  the  meridian 
on  which  are  located  the  fragmentary  outcrops  of  quartzite  which 


210  REPORT  OP  THE  VERMONT   STATE  GEOLOGIST. 

were  described  for  St.  Albans  Point.  It  seems  likely  that  the 
present  margin  of  overthrust  rocks  north  of  Georgia  is  an  erosion 
trace  of  a  mass  of  older  rocks  that  once  had  an  extension  to  the 
west  of  the  present  western  limit  of  these  rocks  and  that  the  frag- 
ments of  quartzite  now  isolated  within  the  slate  formation  on  the 
St.  Albans  lowland  may  be  really  remnants  of  resistant  members 
of  such  a  mass.  This  seems  probable,  even  though  it  must  be 
recognized  that  the  thrust  of  the  older  rocks  on  the  slates  may  not 
have  carried  them  so  far  west  in  higher  latitudes  as  it  did  in 
Georgia  and  farther  south,  for  which  idea  one  finds  some  support 
in  the  present  northeasterly  trend  of  the  margin  of  these  rocks  in 
northwestern  Vermont  and  in  their  extension  northward  into 
Canada. 

The  Lower  Cambrian  Red  Sandrock  series  of  quartsites  and 
dolomites  and  associated  shales  in  Georgia.  The  massive  gray, 
red,  and  mottled  members  of  the  Red  Sandrock  series  near  the 
lake  in  Georgia  are  indistinguishable  from  the  similar  rocks  in 
the  townships  to  the  north.  They  do  not  appear  to  have  suffered 
any  notable  internal  deformation  and  plainly  dip  at  a  low  angle  to 
the  east.  Away  frofn  the  lake  the  hard  rock  is  more  extensively 
covered  by  surface  material  and  emerges  as  knolls,  hills  and 
ridges  of  varying  dimensions.  Around  Georgia  Plains  and  north- 
ward along  the  headwaters  of  Mill  River  the  underlying  rock  had 
clearly  been  somewhat  dissected  before  the  surface  covering  was 
spread  over  the  region. 

About  a  mile  and  a  half  north  of  Georgia  Plains  and  about 
the  same  distance  east  of  the  lake  is  a  hill  known  to  residents  as 
"Parker's  Ledge."  This  locality  has  long  been  celebrated  for  the 
Lower  Cambrian  fossils  which  have  at  various  times  been  found 
there.  The  farm  of  which  the  hill  forms  a  part  is  now  owned  by 
Mr.  Montcalm.  The  prevailing  rocks  at  the  "Ledge"  are  dense 
black  or  sandy,  often  micaceous,  rusty-weathering  shales,  which 
after  diligent  search  may  now  afford  fragments  of  OleneUus, 
Olenoidcs,  Microdiscus  and  other  fossils.  These  shales  have  great 
similarity  to  the  rocks  of  Swanton  which  lie  to  the  east  of  the 
gray  and  mottled  dolomites  of  that  town  and  like  the  shales  of 
Swanton  have  some  dolomite  associated  with  them.  Some  of  the 
dolomites  at  the  "Ledge"  are  of  gray  color  and  others  are  rusty- 
weathering,  siliceous  rocks.  The  rocks  at  the  "Ledge"  have  for 
the  most  part  a  flattish  position  or  dip  to  the  east  at  a  low  angle. 

A  half  mile  south  of  the  "Ledge"  on  the  farm  of  Mr.  Sart- 
well  quartzitic  shales  are  interbedded  with  dolomite,  but  west- 
ward on  the  Densmore  farm  the  shaly  members  occur  in  greater 
force  and  have  much  similiarity  to  those  at  the  "Ledge."  These 
shales  carry  "fucoidal"  markings,  which  are  probably  trails,  but 
did  not  yield  other  fossils.  They  give  place  westward  at  the 
surface  to  the  gray  and  mottled  members  of  the  Red  Sandrock 
series. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  211 

The  gray  and  mottled  rocks  near  the  lake  in  Georgia  township 
are  thus  seen  to  pass  eastward  at  the  surface  into  somewhat  dif- 
ferent rocks  with  which  they  may  be  conformable.  The  general 
surface  sequence  and  the  dips  of  the  various  rocks  suggest  a  con- 
tinuous stratigraphical  series,  but  it  is  not  certain  that  the  apparent 
conformity  is  everywhere  real  and  that  dislocations  do  not  inter- 
vene among  these  various  rocks  that  seem  with  more  or  less 
definiteness  to  be  of  Lower  Cambrian  age. 

In  the  northern  part  of  the  township  the  dolomites  are  suc- 
ceeded eastward  at  the  surface  along  the  road  crossing  Mill  River, 
which  passes  School  No.  7,  by  sheared  quartzite,  which  also  out- 
crops frequently  along  the  main  highway  from  Georgia  Center 
to  St.  Albans,  to  the  west  of  St.  Albans  Hill.  Similar  rock  out- 
crops around  Georgia  Center ;  but  west  and  southwest  of  Georgia 
Center  the  quartzite  is  intermingled  with  areas  of  limestone  con- 
glomerate presently  to  be  described. 

The  road  running  directly  east  from  Georgia  Center  ascends 
a  slope  over  sheared  quartzite.  There  is  then  an  interval  along 
the  road  of  a  little  less  than  a  mile  with  no  outcrops.  Near  the 
junction  of  this  road  with  one  running  south  past  School  No.  11 
are  numerous  ledges  of  massive  gray  and  mottled  dolomite  clearly 
dipping  westerly.  A  reading  gave  the  dip  as  Z7°  and  the  strike 
as  N.  10°  E.  These  rocks  may  be  followed  northward  and  south- 
ward along  their  strike.  Southward,  about  a  mile  and  a  half 
from  the  junction  of  the  roads  just  mentioned,  massive  dolomite 
was  noted  dipping  westerly,  and  northward,  a  mile  north  of  Oak- 
land, are  similar  rocks  also  dipping  westerly.  The  latter  outcrops 
are  two-thirds  of  a  mile  southwest  of  Bellevue  Hill,  described 
above.  Dolomite  outcrops  along  the  road  on  the  lower  western 
slope  of  Cushman  Hill,  but  is  succeeded  farther  up  the  slope  by 
■quartzite. 

Taking  into  account  the  low  easterly  dip  of  the  members  of 
the  Red  Sandrock  series  at  their  western  margin  and  the  sugges- 
tion of  their  possible  extension  in  that  attitude  eastward  beneath 
the  surface  the  westerly  dips  of  the  rocks  just  described  might 
seem  to  show  that  the  beds  in  question  form  a  broad,  shallow 
syncline  over  most  of  Georgia  township  west  of  the  C.  V.  R.  R. 
track.  It  is  possible  that  they  do  and  that  the  higher  dips  at  the 
east  represent  a  pushing  up  of  the  eastern  limb,  with  crushing 
at  some  places  (Bellevue  Hill).  The  massive  beds  ruptured 
instead  of  folding,  the  rocks  east  of  the  railroad  track  now  oc- 
cupying the  upthrow  side  of  a  reverse  fault-thrust.  But  as  men- 
tioned above  it  is  not  certain  that  dislocations  do  not  intervene 
between  the  western  margin  and  the  railroad  track,  so  that  it  can- 
not be  positively  stated  that  Georgia  shales  are  conformably  above 
the  dolomite  series  near  the  lake,  although  they  seem  to  be. 

The  limestone  conglomerate  jormation  in  Georgia.  In 
Georgia  the  most  conspicuous  outcrops  of  the  conglomerate,  or  of 


212  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

liriiestone  that  is  apparently  to  be  correlated  with  it,  occur  west 
of  Georgia  Center  and  east  and  southeast  of  Georgia  Plains.  On 
account  of  surface  covering  the  outcrops  are  intermittent  and  of 
variable  extent  in  present  surface  exposure.  West  of  Georgia 
Center  the  conglomerate  has  all  the  essential  features  of  the  rock 
in  St.  Albans  and  Swanton.  It  carries  abundant  limestone  frag- 
ments of  dilterent  sizes  in  a  matrix  of  strongly  siliceous  material 
which  has  enough  calcareous  matter  to  effervesce  freely  with  acid. 

Dr.  Walcott  in  his  early  account  of  the  Georgia  section  de- 
scribed the  conglomerate  as  apparently  forming  a  great  lenticular 
mass  of  limestone,  with  intercalated  beds  of  argillaceous  shales, 
and  more  rarely  with  arenaceous  layers  imbedded  in  the  argil- 
laceous shales.  The  fauna  was  described  as  Cambrian  in  char- 
acter, and,  in  the  absence  of  Olenellus  and  other  typical  Lower 
(then  called  Middle)  Cambrian  fossils,  as  approaching  the  Upper 
Cambrian.^  In  his  diagram  of  the  Georgia  section,  Walcott 
shows  the  conglomerate  formation  as  an  interbedded  member  of 
the  Georgia  series.  In  referring  to  the  vertical  distribution  of 
the  fossils  (loc.  cit.,  p.  20)  he  remarks  that  one  species  of  the 
typical  Georgia  fauna.  Ptychoparia  adamsi,  "is  represented  in  the 
great  'lentile'  of  the  Georgia  section,"  but  he  drew  the  provisional 
upper  line  of  the  Georgia  Formation  at  the  base  of  the  lentile,  as 
it  is  at  this  horizon  that  there  occurs  a  decided  change  in  fauna 
and  that  the  deposit  changes  markedly  from  that  below. 

Several  years  later,^  after  the  recognition  of  the  Lower 
Cambrian  age  of  the  Georgia  shales  (the  fauna  of  these  shales 
having  been  regarded  by  Walcott  in  his  earlier  studies  [1886]  as 
Middle  Cambrian)  Dr.  Walcott  reproduced  his  early  diagram 
of  the  Georgia  section,  showing  the  conglomerate  as  an  inter- 
bedded member  of  the  Georgia  series  and  stated  that  it  contains 
a  fauna  that  may  jDrove  to  be  of  Middle,  or  possibly  Upper  Cam- 
brian age. 

In  commenting  on  the  Georgia  section  as  late  as  1911,^  Ulrich 
said :  "The  base  of  the  section  is  here  unknown.  As  worked  out 
by  Walcott,  the  lowest  exposed  formation  is  a  limestone  1,000 
feet  thick.  This  is  succeeded  by  200  feet  of  'Georgia  shale,'  and 
over  this  comes  3,500  feet  of  shale  and  thin  limestone.  A  quartz- 
ite  50  feet  thick  follows  and  is  in  turn  overlain  by  1,700  feet  of 
limestone  and  shale,  and  this  by  3,500  feet  of  shale.  I  have  seen 
only  the  upper  part  of  this  section,  namely,  the  heavy  bed  of 
shale  last  mentioned,  which,  together  with  all  the  underlying  beds 
has  been  referred  to  the  Lower  Cambrian  by  Walcott.  Regarding 
the  upper  shale  I  am  strongly  inclined  to  view  it  as  of  Canadian 
age  rather  than  Cambrian.  There  is  some  question  in  my  mind, 
also,  concerning  the  age  of  the  limestone  supposed  to  belong  to 
the  1,700-foot  bed.     It  contains  small  bivalved  phyllopods  {e.  g., 

1  Bull.  U.   S.  G.   S.  No.  30,  1886,  p.   17. 

'Tenth  Annual  Rept.,  Director  U.   S.  G.  S.,  1890,  pp.  553-554. 

3  Revision  of  the  Paleozoic  Systems,  Bull.  G.   S.  A.  No.  22,  1911,  p.   617. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  213 

Indiana  dcnnatoides  (Walcott),  /.  pyriformis  Matth.,  /.  secunda 
M.,  Bradoria  scrutata,  M.)  which  are  characteristic  of  Lower 
Acadian  zones  in  New  Brunswick  and  Newfoundland.  As  it  is 
not  yet  decided  whether  the  Protolenus  zone  is  late  Lower  Cam- 
brian or  early  Middle  Cambrian,  the  exact  age  of  the  Vermont  bed 
mentioned  also  remains  uncertain."  He  then  comments  on  the 
complicated  structure  of  Vermont  rocks  and  of  those  of  the 
Taconic  area  in  particular. 

In  the  writer's  studies  of  the  structural  relations  of  these 
rocks  it  was  not  possible  to  show  that  the  conglomerate  is  inter- 
bedded  in  the  shale  series,  or  that  it  could  not  be  interpreted  as 
resting  unconformably  upon  eroded  rocks. ,  The  field  relations 
leave  much  uncertainty  as  to  the  stratigraphic  relations  of  the 
conglomerate  to  the  rocks  with  which  it  is  associated  in  Georgia. 
If  the  conglomerate  lies  in  a  broad,  open  syncline  of  Lower  Cam- 
brian rocks  it  might  be  interpreted  structurally  as  belonging  to 
any  formation  later  than  Lower  Cambrian,  and  if  its  fossils  are 
truly  Middle  or  still  later  Cambrian  they  might  be  regarded  as 
forming  a  primary  fauna,  or  as  secondarily  included  in  a  later 
terrane  by  erosion  of  Middle  or  later  Cambrian  rocks. 

Fairfax  Township. 

(St.  Albans  and  Milton  topographic  sheets.) 

This  township  bounds  Georgia  on  the  east. 

Near  the  summit  of  Cushman  Hill,  about  two-thirds  of  a 
mile  north  of  Silver  Lake  and  just  east  of  the  Georgia  line,  the 
present  surface  apparently  marks  erosion  into  the  lower  portions 
of  an  overlapping  formation.  At  numerous  outcrops  the  rock, 
which  may  be  a  rusty,  impure  quartzite  or  a  greenish-gray,  schist- 
ose quartzite,  carries  scattered  large  grains  qr  rounded  pebbles  of 
grayish-white  quartz.  In  dimensions  these  pebbles  range  from 
the  size  of  a  marble  to  that  of  an  Q.gg.  The  pebbles  are  apparently 
not  sheared,  but  the  rock  in  which  they  are  included  is  sometimes 
schistose. 

The  significance  of  this  imperfectly  developed  conglomerate 
and  the  obvious  impurity  of  its  matrix  in  places  seems  to  be  that 
the  rocks  of  this  higher  land  are  not  a  great  way  above  or  distant 
from  the  old  sea-floor  on  which  the  series  of  which  they  are  a 
part  was  deposited ;  but  no  unconformable  contacts  nor  any  recog- 
nizable older  rocks  were  seen.  The  conglomerate  is  not  purely 
local,  for  similar  rock  was  observed  three  miles  farther  east  in 
Fairfax,  near  Buck  Hollow,  and  five  miles  to  the  north  in  St. 
Albans,  and  also  at  the  northern  end  of  Bellevue  Hill.  The  con- 
glomerate is,  however,  everywhere  local  in  the  sense  that  it  grades 
laterally  into  impure  quartzite,  or  derivatives  of  impure  sands. 
It  is,  therefore,  intraf ormational  in  this  sense ;  it  is  basal  only  in 
the  same  general  sense.     It  indicates  particular  local  conditions  of 


214  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

deposition  and  perhaps  minor  oscillations.  It  can  hardly  be 
interpreted  as  forming  residuary  parts  of  a  formation  that  rested 
unconformably  upon  the  other  rocks  with  which  it  is  now  asso- 
ciated. 

At  the  northern  end  of  Georgia  Mountain,  in  the  southeastern 
part  of  the  township,  along  the  hill  road  running  east,  south  of 
the  Lamoille  River,  are  outcrops  of  gneissic-looking  rocks  with 
foliations  dipping  easterly  at  a  high  angle.  On  their  weathered 
surfaces,  and  on  vertical  joint  or  fracture  planes  across  the  strike, 
these  rocks  give  somewhat  the  appearance  of  squeezed  conglo- 
merates with  the  foliations  bending  gently  around  squeezed  frag- 
ments ;  but  the  latter,  on  close  inspection,  have  little  appearance 
of  pebbles  distinct  from  a  matrix,  and  when  the  rock  is  broken 
it  looks  much  like  somewhat  impure  quartzite.  On  the  whole  the 
rock  most  suggests  a  sheared  and  welded  quartzite,  whose  resist- 
ance to  deformation  resulted  first  in  shearing  and  brecciation. 
The  rock  was  then  healed  and  compacted  into  a  gneiss.  The  rocks 
are  succeeded  eastward  by  outcrops  of  granular  quartzite. 

CHITTEJfDEN  COUNTY. 

Milton  Township. 

(Milton  topographic  sheet.) 

Location.  Milton,  another  lake  shore  township,  lies  just 
south  of  Georgia.  The  southern  boundary  of  Georgia  forms  the 
northern  boundary  of  Milton,  throughout  its  extent.  Westford 
lies  to  the  east  and  Colchester  borders  it  on  the  south. 

The  lake  border  in  Milton  tozvnship.  The  escarpment, 
capped  by  the  massive  beds  of  gray,  red  and  mottled  dolomites, 
which  closely  follows  the  lake  shore  in  Georgia  and  part  of  St. 
Albans  continues  southward  into  Milton.  In  Milton,  as  in 
Georgia,  younger  gray  limestones  and  slate  or  outcrops  of  slate 
alone  intervene  between  the  margin  of  the  Red  Sandrock  series 
and  the  lake  shore. 

North  of  Camp  Rich,  gray  limestone  occurs  between  out- 
crops of  slate  in  the  shore  road  and  the  margin  of  the  Red  Sand- 
rock  series.  South  of  the  camp,  towards  Camp  Watson,  the 
margin  of  the  Cambrian  rocks  more  closely  approaches  the  shore 
and  outcrops  of  gray  limestone  are  fewer.  The  shore  road  from 
Camp  Rich  to  Camp  Watson  is  nearly  all  the  way  on  the  slates 
which  continue  south  to  Eagle  Mt.  Camp  at  the  mouth  of  Stone 
Bridge  Brook. 

South  of  the  mouth  of  Stone  Bridge  Brook,  Eagle  Mt.  rises 
to  a  height  of  500  feet.  It  is  composed  of  the  massive  dolomites 
of  the  Red  Sandrock  series  and  has  a  steep  scarp  on  the  west 
which  was  estimated  in  some  places  to  be  200  or  more  feet  high. 
The  Cambrian  rocks  continue  southward  with  somewhat  dimin- 
ished but  still  conspicuous  scarp  to  the  vicinity  of  Camp  Martin 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  215 

(generally  known  as  Camp  Milton).  Between  Eagle  Mt.  Camp 
and  Camp  Milton  the  margin  of  the  Canibrian  rocks  is  perhaps 
300  feet  from  the  lake  and  the  slope  between  is  steeper  than  is 
usual  farther  north,  apparently  largely  on  account  of  large  talus 
blocks  which  have  fallen  from  the  scarp  and  which  are  now  partly 
covered  with  drift.  Between  Eagle  Mt.  Camp  and  Camp  Milton 
the  slate  formation  shows  continuous  outcrop  along  shore  and 
throughout  this  distance  gray  limestone  was  not  noted  between 
the  shore  and  the  scarp,  except  just  north  of  Camp  Milton. 

East  of  Camp  Milton  is  an  erosion  gap  in  the  margin  of  the 
Red  Sandrock  series.  Trout  Brook  flows  along  the  southern 
margin  of  this  gap  to  enter  the  lake. 

The  indication  is  strong  that  between  Eagle  Mt.  Camp  and 
Camp  Milton  the  Red  Sandrock  series  frequently,  if  not  usually, 
rests  on  the  slates.  Just  north  of  the  mouth  of  Stone  Bridge 
Brook  the  slates  form  isolated  shore  cliffs  50  feet  high  without 
any  traces  of  overthrust  rock  resting  on  them.  Just  south  of  the 
mouth  of  the  brook  the  massive  dolomite  of  the  Red  Sandrock 
formation  reaches  close  to  the  water  edge  with  only  a  high  water 
or  storm  beach  of  slate  shingle  between  it  and  the  shore,  no  out- 
crops of  slate  or  other  rock  being  visible.  The  topography  and 
geology  suggest  a  fault  along  the  gap  mentioned  above,  the  rocks 
at  the  north  occupying  the  upthrow  side.  The  dolomite  continues 
south  along  the  eastern  edge  of  the  swampy  delta  of  the  Lamoille 
River  to  the  delta  portion  of  the  Sandbar  Bridge  road,  showing 
as  a  low  cliff  of  varying  height,  to  the  east  of  which  the  surface 
ascends  over  the  eroded  edges  of  other  members  of  the  Red 
Sandrock  series.  South  of  the  delta  road  the  erosion  margin  of 
the  overthrust  dolomite  series  is  less  easily  followed  to  the  bank 
of  the  Lamoille  River. 

Between  Trout  Brook  and  the  Lamoille  the  dolomite  prob- 
ably rests  on  the  slates  just^as  it  does  at  Red  Rock  Point  near 
Malletts  Bay  in  Colchester. 

The  steep  western  face  of  Eagle  Mt.  gives  suggestion  of 
what  the  faded  scarp  all  along  the  margin  of  the  Cambrian  Red 
Sandrock  formation  may  once  have  been.  It  seems  quite  likely 
that  the  erosion  modification  of  these  resistant  rocks  along  their 
present  trace  was  subsequent  to  the  formation  of  the  lowland  in 
the  weaker  shales  and  limestones  in  what  is  now  the  lake  region. 
It  is,  however,  not  apparent  from  the  present  relations  of  these 
various  rocks  how  far  the  Red  Sandrock  may  have  extended  to 
the  west  of  its  present  erosion  trace.  It  is  interesting  to  note  that 
in  some  places  the  Cambrian  rocks  rest  by  thrust  on  limestone  and 
at  other  places  on  shales  or  slates  that  are  younger  than  the  lime- 
stone. Such  relations  should  have  something  to  say  about  the 
mode  of  deformation  by  which  the  present  relations  could  have 
been  produced. 


216  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Just  east  of  the  road  that  runs  from  Camp  Milton  eastward, 
about  half  a  mile  from  the  lake  shore,  a  ledge  of  brick-red 
quartzite-dolomite  displays  a  texture  which  differs  strikingly 
from  that  which  the  mottled  "Swanton  marble"  member  of  the 
Red  Sandrock  series  shows.  The  rock  as  a  whole  forms  a  mass- 
ive bed  in  which  may  be  clearly  seen  many  angular  fragments  of 
different  sizes,  including  blocks  of  rectangular  shape  as  seen  in 
section  which  bear  strong  resemblance  to  similarly  shaped  frag- 
ments seen  in  the  limestone  conglomerate  formation.  Moreover, 
the  angular  pieces  are  mingled  with  other  larger,  irregularly 
shaped  chunks,  giving  an  assemblage  like  that  in  much  of 
the  limestone  conglomerate.  The  fragments  are,  however,  of 
much  the  same  color  as  the  rest  of  the  rock  and  apparently  are 
composed  of  a  material  similar  to  the  matrix  in  which  they  lie. 
From  the  conditions  it  is  not  possible  to  tell  whether  the  frag- 
mented rock  is  an  intra forma^ional  conglomerate  or  a  peculiar 
form  of  brecciation.  A  similar  fragmental  rock  of  gray  dolomite 
occurs  west  of  Checkerberry  village  and  will  be  mentioned  beyond. 

The  west-central  portion  of  Milton  township.  East  of  the 
escarpment  that  borders  the  lake  the  surface  over  the  west-central 
portion  of  Milton  is  largely  formed  of  sand  plains  through  which 
the  hard  rock  emerges  as  dwarf  exposures  which  are  often  frag- 
mentary and  unsatisfactory  for  study.  Arrowhead  Mt.,  Cobble 
Hill  and  the  gorge  of  the  Lamoille  River  give  more  extensive  out- 
crops. 

From  the  escarpment  near  the  lake  the  massive  beds  of  the 
Red  Sandrock  series  extend  eastward  with  low  easterly  dip,  form- 
ing in  the  western  part  of  the  township  a  fairly  well  defined  band 
of  varying  breadth  from  the  Georgia  line  to  the  Lamoille  River. 
East  of  this  band  the  members  of  the  series  lose  distinctness  as 
one  passes  into  the  areas  of  more  scattered  outcrops  of  the  west- 
central  part.  Between  the  western  band  just  mentioned  and  an- 
other strip  to  the  east  that  includes  Arrowhead  Mt.,  the  village 
of  Milton  and  Cobble  Hill,  the  exposures  are  prevailingly  gray 
dolomitic  rock,  rather  sparingly  associated,  so  far  as  the  rocks  are 
visible,  with  a  more  quartzitic  rock,  without  any  very  clear  struc- 
tural relations  between  the  two.  Some  of  the  outcrops  may  now 
be  mentioned. 

North  of  the  Lamoille  River,  to  the  east  and  west  of  Streeter 
Brook,  are  numerous  outcrops  of  gray  dolomite  which  give  way 
at  places  along  the  strike  to  quartzite.  The  relations  suggest  either 
that  dolomite  grades  laterally  into  quartzite,  or  that  different  but 
conformable  beds  are  exposed  in  different  outcrops.  Either  inter- 
pretation seems  possible,  if,  as  seems  likely,  the  rocks  are  to  be 
correlated  in  a  general  way  with  the  members  of  the  series  along 
the  lake.  By  such  correlation  is  not  meant  precise  stratigraphic 
equivalence,  but  membership  in  a  common  formation  which  gives 
good  indications  that  horizontal  variation   in   its   different  beds 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  217 

was  a  common  if  not  a  usual  condition  and  that  dolomites  and 
more  siliceous  beds  succeeded  one  another  in  a  more  or  less 
regular  fashion  within  the  formation. 

From  Milton  village  to  the  lake  the  Lamoille,  in  sinking  its 
channel  since  glacial  times,  has  cut  through  hard  rock  at  many 
places,  producing  a  considerable  fall  near  Milton  village  and 
minor  ones  farther  west.  The  rocks  which  the  river  has  thus  cut 
through  show  some  interesting  differences. 

At  West  Milton  the  river  cuts  massive  gray  dolomite,  which 
outcrops  in  both  banks  and  in  midstream.  A  mile  above  this 
village  the  rock  is  more  notably  siliceous.  These  rocks  appear  to 
be  the  southward  continuation  of  those  lying  west  of  Streeter 
Brook,  to  the  north.  Farther  up  stream,  from  the  point  where 
Streeter  Brook  enters  the  Lamoille  to  the  abutments  of  the  old 
stage  road  bridge  near  the  Milton  Town  Farm,  the  rock  along  the 
stream  is  a  slate,  with  easterly  dipping  cleavage.  Where  worn  by 
the  water  the  rocks  often  show  pseudolaminations  probably  cor- 
responding with  the  cleavage.  At  places  above  the  high-water 
mark  the  rock  is  often  a  dense  slate.  The  river  cascades  approx- 
imately along  the  strike  over  these  slates  beloM^  the  old  bridge  site, 
forming  what  are  frequently  called  by  the  residents  the  "minor 
falls."  The  slates  continue  upstream  towards  Milton  village  and 
seem  to  pass  beneath  other  rocks  forming  the  upper  falls  at  the 
mill  of  the  International  Paper  Company.  The  slates  near  the 
upper  falls  have  been  jammed  and  sheared  with  obliteration  of 
bedding  and  folded  structure.  Folding  was  seen  at  only  one 
place.  Induration  is  the  rule.  The  rock  which  apparently  over- 
lies the  slate  at  the  upper  falls  is  a  somewhat  indeterminate  mass 
of  gray  dolomite  and  quartzite.  At  some  places  the  rock  shows 
a  texture  precisely  like  the  "Swanton  marble,"  but  without  the 
conspicuous  variegated  coloration.  For  the  most  part  the  rocks 
resemble  the  members  of  the  Cambrian  series  near  the  lake. 
They  are  generally  massive  in  present  appearance,  although  there 
are  observable  planes  of  separation  which  may  represent  bedding 
or  jointing.  At  the  falls  the  massive  rocks  are  cut  by  a  dike  4 
to  8  inches  wide  running  across  the  strike.  A  dike  of  similar 
rock,  with  apophyses,  cuts  the  slates  just  west  of  the  mouth  of 
Streeter  Brook.  The  rock  that  makes  the  falls  continues  as  a 
scarp  into  the  woods  north  of  the  falls.  The  general  relations- 
suggest  that  the  dolomites  have  been  pushed  over  the  slates  that 
lie  under  and  west  of  them. 

Upstream  above  the  falls,  well  shown  both  above  and  below 
the  bridge  and  sparingly  along  the  streets  in  the  village  near  the 
bridge,  is  indurated  quartzite. 

Southwest  and  west  of  Milton  village,  south  of  the  Lamoille. 
is  a  broad,  flat,  sand  plain  with  no  outcrops  except  at  its  western 
edge,  west  of  Checkerberry  village.  A  half  mile  northwest  of 
this  hamlet,  low  ledges  of  dolomite  show  the  peculiar  conglom- 


218  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

erate  or  "brecciated"  texture  noted  in  previous  pages  as  occur- 
ring in  a  reddish  bed  of  the  Sandrock  series  near  the  lake,  in  the 
Hmestone  conglomerate  and  in  the  gorge  at  Highgate  Falls. 

North  of  the  Colchester  line  and  east  of  the  road  from 
Checkerberry  village  to  School  No.  9,  is  gray  dolomite  dipping 
easterly.  This  rock  continues  easterly  across  the  road  that  runs 
west  of  Cobble  Hill,  but  on  the  western  slope  of  the  hill  the 
dolomite  is  marked  by  frequent  inclusions  of  chert  and  lies  at 
the  base  of  a  modified  but  still  notable  scarp  in  the  schistose 
quartzite  that  makes  up  the  principal  portion  of  Cobble  Hill  and 
that  outcrops  north  of  it  and  along  the  road  that  skirts  it  on  the 
east. 

North  of  Milton  village  the  Lamoille  is  deflected  to  a  south- 
ward course  by  the  mass  of  Arrowhead  Mt.  which  rises  to  a 
height  of  947  feet  and  forms  a  conspicuous  feature  of  the  town- 
ship. The  eastern  slope  of  this  mass  shows  gray  dolomite  and 
quartzite,  often  sheared,  but  at  places  showing  clearly  defined 
westerly  dip.  The  westerly  dip  is  conspicuous  at  the  southern 
end  of  the  mountain  proper.  West  of  Arrow  Mt.,  along  the 
road  at  the  western  base,  are  black,  fine-grained,  siliceous  slates. 

South  of  Arrowhead  Mt.,  and  about  a  mile  north  of 
Milton  village,  quartzite  forms  bold,  massive  ledges  west  of  the 
Georgia  road.  The  quartzite  beds  have  been  sheared  so  as 
to  give  a  more  massive  appearance  than  they  really  possess,  a 
feature  common  among  these  rocks  in  which  shearing  has  welded 
not  always  especially  heavy  beds  into  very  massive  looking  rocks. 
The  quartzite  just  mentioned  joins  southward  with  that  above  the 
falls  in  the  village. 

A  broad  surface  section  from  the  river  in  Milton  village  east- 
ward along  the  road  to  School  No.  6,  shows  that  the  quartzite  at 
the  river  is  succeeded  eastward  by  gray  dolomite  and  quartzite 
which  form  a  low  ridge  just  east  of  the  railroad  track.  The  rocks 
are  sheared  but  at  places  show  a  westerly  dip.  As  one  ascends 
the  hilly  land  east  of  the  village,  dolomite  and  quartzite  roughly 
alternate  across  the  strike  on  the  lower  portion  of  the  slope ;  but 
higher  up  the  slope  dolomite  is  absent  and  much  of  the  rock, 
while  apparently  originally  a  quartzite,  shows  a  gneissoid  struc- 
ture like  that  which  has  been  described  for  the  northern  end  of 
Georgia  Mt.  The  rock  sometimes  shows  the  bedding  across 
which  the  gneissoid  structure  has  been  developed.  The  gneissoid 
rock  is  succeeded  eastward  by  ledges  of  not  severely  sheared 
quartzite,  which  may  be  seen  in  the  vicinity  of  School  No.  6. 
At  some  places  the  quartzite,  including  that  which  has  been 
sheared  into  a  gneiss,  is  disposed  in  gentle  folds. 

The  gneissoid  rock  might  be  regarded  by  some  observers 
as  something  dififerent  from  the  quartzite  with  which  it  is  asso- 
ciated, but  there  are  no  contacts  nor  other  field  relations  suggest- 
ing that  the  rocks  are  members   of   different   formations.     The 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  219 

possibility  that  older  rocks  might  have  been  thrust  into  the  quartz- 
ite  formation  must  be  recognized ;  but  when  the  gneissoid  struc- 
ture appears  in  a  bedded  quartzite  and  when  the  quartzitic  char- 
acter of  other  gneissoid  rock  is  so  obvious  and  no  valid  distinctions 
may  be  made  among  numerous  exposures  over  large  open  fields, 
the  membership  of  these  different  rocks  in  a  common  formation 
seems  the  ready  and  reasonable  interpretation  and  the  differences 
seem  to  be  explainable  as  due  to  various  degrees  of  shearing  and 
primary  difTerences  in  composition. 

The  quartzite  and  its  gneissoid  associate  continue  south  from 
the  road  to  School  No.  6  towards  Colchester,  along  the  higher 
portions  of  the  western  slope  of  the  hilly  land ;  but  on  the  lower 
portions  of  the  slope  the  rock  is  quartzite. 

A  section  was  made  along  the  road  that  runs  from  School 
No.  10  to  Bowmans  Corner  in  Westford.  The  quartzite  at  the 
western  base  of  the  hilly  land  continues  to  the  bend  in  the  road 
two  miles  west  of  Bowmans  Corner.  The  rock  is  sheared,  with 
strong  cleavage  dipping  easterly.  South  of  the  road,  at  the  bend 
mentioned,  white  quartzite  is  associated  with  brick-  or  cherry- 
red  quartzite  in  such  relations  as  to  indicate  that  the  two  rocks 
are  lateral  color  variants  of  each  other.  Eastward  along  and 
south  of  the  road  to  Bowmans  Corner  are  frequent  ledges  of  gray 
siliceous  dolomite  which  is  more  or  less  intermingled  over  large 
areas  with  quartzite  and  this  quartzite-dolomite  series  extends 
eastward  nearly  to  the  corner. 

From  the  descriptions  which  have  been  given  it  will  be  seen 
that  much  the  same  kinds  of  rocks  and  structures  occur  in  Milton 
as  in  Georgia.  Near  the  lake  the  members  of  the  Red  Sandrock 
series  dip  easterly  at  a  low  angle.  Farther  east  are  dolomites 
and  quartzites  in  scattered  outcrops  which  apparently  belong  to 
the  same  formation.  Along  meridians  passing  through  and  east 
of  Milton  similar  rocks  show  westerly  dip  at  many  places  or  are 
apparently  broken  and  thrust  on  rocks  lying  west  of  them.  Most 
of  the  rocks  so  far  mentioned  probably  belong  to  the  same  general 
formation  in  which  there  are  differences  among  the  beds  due  to 
primary  horizontal  and  vertical  variations  and  to  secondary  shear- 
ing effects.  It  appears  that  the  underlying  hard  rock  away  from 
the  lake  shore  in  Milton  is  probably  essentially  a  Lower  Cambrian 
surface  as  is  the  case  in  Georgia.  There  are,  however,  among 
these  rocks  some  others  which  are  not  easily  correlated  with  them, 
such  as  the  slates  found  along  the  course  of  the  Lamoille  River, 
west  of  Milton. 

Certain  rocks  in  Westford  tozvnship,  adjoining  Milton  on  the 
east.  At  Bowmans  Corner  and  along  the  road  towards  Essex 
Junction  is  greenish  slate  or  phyllite  which  over  long  distances  is 
more  or  less  interchangeable  with  quartzite.  The  greenish  slate 
shows  coppery-colored  phyllitic  and  schistose  variants  and  all  have 


220  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

a  good  deal  of  similarity  to  similarly  associated  rocks  at  some 
places  in  the  Taconic  hills  many  miles  to  the  south. 

A  section  along  the  road  from  Milton  village  by  the  Hard- 
scrabble  School  to  Westford  gives  quartzite  at  the  western  base 
of  the  hilly  land,  then  farther  up  the  hill  the  gneissoid  quartzite, 
then  a  wide  band  of  greenish  slate,  which  is  the  northern  exten- 
sion of  that  near  Bowmans  Corner  and  then  around  Westford 
village  quartzitic  schist  which  was  followed  over  the  high  land 
southwest  of  Westford  village  along  the  road  to  Essex  Center  by 
the  Beecher  School.  At  the  east  the  quartzitic  schist  frequently 
carries  segregated  quartz  and  as  a  mass  strongly  resembles  similar 
rocks  found  in  the  Sudbury  Hills.  • 

The  limestone  conglomerate  formation  in  Milton.  The  ex- 
tensive sand  plains  in  Milton  probably  conceal  some  of  this 
formation.  South  of  the  hamlet  of  West  Georgia,  but  south  of 
the  Georgia  line,  are  a  few  scattered  ledges  of  rock,  some  of 
which  bear  such  close  resemblance  to  thinly-bedded  limestone 
members  of  the  conglomerate  formation  in  Highgate  and  St. 
Albans  that  there  is  little  doubt  as  to  their  correlation  with  each 
other.  The  exposures  are  few  and  were  the  only  ones  seen  in 
Milton  except  some  fragmentary  rocks  found  seven  miles  to  the 
southeast,  near  School  No.  3,  about  a  mile  north  of  the  Colchester 
line.  At  the  latter  place,  east  of  Malletts  Creek  and  the  railroad 
track,  are  a  few  ledges  of  limestone,  some  of  which  resemble  those 
found  to  the  north.     No  conglomerate  was  seen. 

Colchester  Township. 

(Plattsburg,  Milton  and  Burlington  topographic  sheets.) 

Location.  This  township  is  bounded  on  the  north  by  Milton, 
on  the  east  by  Essex,  and  on  the  south  by  Burlington  and  South 
Burlington. 

The  rocks  along  and  near  the  lake  shore  in  Colchester.  In 
Colchester  township  along  what  is  now  the  border  of  the  lake, 
pre-glacial  erosive  processes  had  breached  the  massive  dolomites 
of  the  Red  Sandrock  series,  producing  a  considerable  basin  which 
is  now  flooded  by  the  lake  waters  and  is  known  as  Malletts  Bay. 

North  of  Malletts  Bay,  between  it  and  the  Lamoille  River, 
various  knolls  and  ridges  give  extensive  outcrops  of  the  members 
of  the  Sandrock  series  which  have  been  traced  from  St.  Albans 
along  the  margin  of  the  lake.  The  erosion  margin  of  these  rocks 
may  be  followed  south  from  the  Lamoille,  east  of  Camp  Winnis- 
quam,  to  Red  Rock  Point,  where  the  formation  dips  into  the  lake. 
North  of  Red  Rock  Point  the  slates  show  in  cliffs  and  low  out- 
crops along  shore  and  at  Clay  Point  form  a  pinnacle  capped  by 
Champlain  clays.  About  200  rods  north  of  Red  Rock  Point, 
massive  dolomite  may  be  seen  in  contact  with  the  slates. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  221 

Around  the  bays  and  headlands  of  the  serrated  north  shore 
of  the  Bay  and  nearly  to  its  eastern  limit  are  perpendicular  or 
rugged  clififs  of  gray  or  mottled  dolomite  much  like  that  at  Red 
Rock  Point.  Similar  rock  outcrops  along  the  road  from  Camp 
Winnisquam  to  the  Colchester-Grand  Isle  road.  The  dip  is 
easterly. 

In  a  minor  indentation  at  the  northeastern  portion  of  the  bay 
is  a  beach  of  sand  at  the  edge  of  a  swamp  that  marks  the  southern 
end  of  a  small  valley.  In  the  western  wall  of  this  valley  the 
rocks  are  massive  but  apparently  in  somewhat  thinner  beds  than 
those  farther  west  and  display  the  reddish  and  pinkish  colors 
characteristic  of  the  Sandrock  series  farther  north.  On  the 
east  side  of  the  valley  the  rocks  are  prevailingly  quartzitic  and  in 
thinner  beds,  which  weather  white,  gray  and  rusty  brown.  Fos- 
sils were  sought  in  the  rusty  layers,  but  without  success.  In  some 
of  these  rocks  around  Malletts  Bay  the  late  Mr.  Griffin  of  the 
Survey  had  found  Olenellus  and  other  fossils,  but  unfortunately, 
his  localities  have  not  all  been  described  in  print.  A  low  scarp 
which  bounds  these  quartzite  beds  on  the  west  continues  south- 
ward along  the  eastern  edge  of  the  swampy  land  and  along  the 
eastern  shore  of  the  lake  north  of  the  mouth  of  Aliens  Brook. 
Along  this  scarp  may  be  seen  lateral  variations  in  l:he  colors  and 
thicknesses  of  the  beds.  The  quartzite  continues  south  of  Aliens 
Brook  to  the  sandy  beach  that  borders  the  bay  on  the  southeast 
and  south. 

West  of  the  sandy  beach  on  the  southern  side  of  the  bay  a 
peninsula  known  as  Coates  Island  juts  into  the  bay.  West  of  the 
'Tsland"  and  separated  from  it  by  a  small  bay  is  a  peninsula 
known  as  Malletts  Head  which  projects  northward  to  within 
about  one-half  mile  of  Red  Rock  Point  and  somewhat  to  the  west 
of  it.  The. head  forms  a  remnant  of  an  old  erosion  margin  of 
the  Red  Sandrock  which  was  breached  to  form  the  bay.  On  the 
western  shore  of  the  Head  the  Ordovician  slates  underlie  the 
dolomite  which  forms  the  surface  rock  of  most  of  the  peninsula. 
The  relations  at  the  head  are  entirely  similar  to  those  north  of 
Red  Rock  Point,  and  there  is  little  doubt  that  slate  lies  beneath 
the  portion  of  the  lake  forming  the  inlet  to  the  bay;  but  whether 
slate  underlies  any  considerable  part  of  the  bay  as  the  hard  rock 
surface  may  only  be  conjectured. 

The  Red  Sandrock  lying  on  the  slate  on  the  western  side  of 
Malletts  Head  is  two-thirds  of  a  mile  west  of  that  at  Red  Rock 
Point,  and  unless  there  is  a  fault  between,  this  fact  points  to  a 
former  more  westerly  extension  of  the  dolomites  farther  north, 
confirming  in  a  measure  the  suspicion  that  the  margin  of  the 
Sandrock  at  least  for  some  of  its  course  north  of  Malletts  Bay  is 
a  recession  border. 

The  rocks  of  Colchester  peninsula,  west  of  the  meridian  of 
Malletts  Head,  to  the  north  of  the  Winooski   River,  were  not 


222  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

inspected  by  the  writer.  The  map  of  the  Vermont  Report  shows 
most  of  the  peninsula  as  underlain  by  "Utica"  or  "Hudson  River" 
slates  and,  therefore,  as  not  having  any  of  the  Sandrock  on  it 
much  to  the  west  of  the  meridian  of  Malletts  Head. 

The  Sandrock  of  Malletts  Head  and  Coates  Island  is  sepa- 
rated from  other  exposures  of  this  formation  lying  south  of  them 
by  a  sand  plain,  the  extension  of  which  eastward  and  southward 
forms  a  wide,  sandy,  partly  swampy  tract  stretching  from  the 
sandy  beach  that  makes  the  southern  border  of  Malletts  Bay  to 
the  Winooski  River.  Along  the  eastern  border  of  this  tract, 
around  the  Colchester  Town  Farm,  are  outcrops  of  the  Sandrock 
formation  which  are  the  southward  continuation  of  the  beds 
forming  the  east  shore  of  Malletts  Bay. 

The  altogether  remarkable  vertical  variations  shown  by  the 
quartzite-dolomite  series  known  in  this  region  collectively  as  the 
■Red  Sandrock  has  been  described  by  Professor  Perkins  from  his 
own  detailed  studies  and  those  of  his  assistant,  the  late  Dan 
Griffin.^  Differences  in  composition,  thickness  and  color  appear 
in  irregular  but  frequent  succession  between  and  within  the  dif- 
ferent beds  along  different  sections  through  the  formation. 
Lateral  variations  with  respect  to  composition  and  color  may  also 
be  seen  when  the  beds  of  this  formation  are  followed  along  their 
strike.  Impure  sands,  fairly  pure  sands  and  sandy  muds  seem  to 
have  been  contemporaneous  with  each  other  and  often  at  places 
not  very  far  removed  from  one  another  during  the  deposition  of 
these  rocks.  Many  of  the  beds  give  clear  evidence  of  shallow 
water  accumulations,  probably  on  a  slowly-subsiding  sea-bottom 
and  one  which  underwent  intermittent  oscillation  of  level.  Red- 
dish shades  of  color,  probably  due  to  oxidation  under  atmos- 
pheric exposure,  frequent  cross  bedding,  and  many  markings  that 
seemingly  could  have  been  produced  only  in  relatively  shallow 
waters,  or  on  exposed  flats,  all  bear  testimony  to  the  nature  of 
the  conditions  under  which  these  rocks  were  laid  down. 

There  seems  to  be  good  reason  for  thinking  that  large  areas 
of  this  Red  Sandrock  formation  once  formed  a  surface  of  ero- 
sion and  unconformity  on  which  other  strata  were  deposited ; 
but  it  is  extremely  doubtful  if  any  considerable  portion  of  such 
surface  is  anywhere  now  preserved  over  the  region  where  this 
formation  makes  the  outcropping  rock.  With  the  facts  in  mind 
that  the  color  variations  which  are  assumed  to  be  due  to  some 
degree  of  oxidation  of  the  material  of  the  rock  are  repeated 
throughout  considerable  vertical  distances  in  this  Red  Sandrock 
series  and  that  lateral  variations  occur  within  continuous  beds; 
that  large  exposures  of  this  formation  at  the  present  surface  hold 
to  a  faiVly  uniformly  gray  color  which  is  presumably  a  primary 
feature ;  and  that  thrusting  has  doubtless  tended  at  least  to  pro- 
duce an  imbricating  rather  than  a  conformable  series  in  the  forma- 

1  Sixth  Rept.  of  the  State  Geol.,  pp.  227  et  seq. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  223 

tion,  as  a  whole  it  is  difficult  to  attribute  the  red  color,  where  this 
may  be  shown  to  be  an  ancient  character  of  the  rock,  as  due  to 
atmospheric  changes  following  the  elevation  and  erosion  of  the 
rocks  subsequent  to  their  deposition  as  a  series.  The  possible 
explanation  of  the  "brecciation"  shown  by  the  mottled  members 
of  this  formation  as  a  primary  feature  has  been  discussed  above. 
All  the  noteworthy  features  of  the  Red  Sandrock  series  are  well 
shown  in  the  vicinity  of  Malletts  Bay. 

The  age  of  this  primarily  conformable  series  has  definitely 
been  made  out  by  the  discovery  of  Olenellus  and  Ptychoparia 
adamsi  in  some  of  the  beds  near  the  bay.^ 

East  of  the  lake  in  Colchester.  East  of  the  lake  much  of 
present  surface  is  formed  of  sand.  Gray  dolomite  or  rusty,  flaggy 
quartzite  outcrop  here  and  there  along  meridians  in  the  central 
part  of  the  township  and  dolomite  and  schistose  quartzite  which 
appear  to  be  interbedded  give  numerous  outcrops  along  the  east 
road  from  Colchester  village  to  Milton.  The  schistose  quartzite 
grades  laterally  into  more  massive  quartzite.  The  prevailing  dip 
is  easterly ;  a  westerly  dip  was  not  noted. 

Two  miles  east  of  the  Town  Farm,  ledges  of  gray  siliceous 
dolomite  carry  bunches  of  segregated  quartz  and  some  lace-like 
tracings  of  silica  on  the  weathered  surface.  These  features  give 
the  rock  an  appearance  somewhat  like  that  shown  by  some  of  the 
rocks  in  Highgate  just  south  of  the  Canada  line,  which  probably 
belong  to  a  Beekmantown  horizon;  but  such  features  are  clearly 
altogether  too  indefinite  for  purposes  of  correlation  and  while 
the  markings  referred  to  were  not  noted  in  the  rocks  near  the 
lake,  they  may  well  be  present  there  and  in  any  event  might  readily 
have  been  produced  by  agents  of  hydrothermal  metamorphism  in 
such  siliceous  rocks.  There  seems  no  good  reason  for  regarding 
these  particular  rocks  as  other  than  Lower  Cambrian. 

A.  mile  east  of  the  Town  Farm  a  quarry  opened  for  road 
metal  shows  beds  of  gray  dolomite  dipping  very  gently  to  the 
east.  Uniformity  of  color  gives  at  first  sight  a  somewhat  massive 
appearance,  but  close  inspection  shows  beds  of  moderate  but 
variable  thickness.  Sections  of  the  bedding  planes,  as  seen  in  the 
face  of  the  quarry  which  was  opened  along  the  strike,  usually 
show  as  ammonoid-suture-like  lines,  often  of  brownish  (limonitic) 
color.  The  bedding  surface  shows  that  these  lines  are  traces  of 
partings  between  irregular  pittings  or  hollows  on  the  surface  of 
one  bed  into  which  project  small  cones  from  the  under  surface  of 
the  overlying  bed.  Separation  of  the  4a-yers  may  sometimes  be 
complete  along  the  pitted  surface  of  the  beds,  but  again  will  be 
accompanied  by  horizontal  fracture  across  the  little  cones  when 
there  will  appear  small  gray  patches  surrounded  by  irregular 
brown  lines.  The  irregular  surfaces  seemed  to  indicate  shallow 
rather  than  deep  water  deposits.     These  rocks  are  a  half  mile 

1  Sixth  Report,  p.  229. 


224  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

or  SO  east  of  the  Red  Sandrock  ledges  near  the  Town  Farm. 
They  are  probably  part  of  the  same  formation. 

In  the  western  part  of  Colchester  village  are  low  ledges  of 
gray  dolomite.  These  rocks  are  on  the  meridian  of  those  in  the 
quarry  mentioned  above.  On  the  same  meridian  farther  north, 
south  and  east  of  Munson  Flat,  are  excellent  exposures  of  rusty, 
flaggy  quartzite  which  carries  obscure  fossil  markings,  but  which 
yielded  nothing  definite. 

The  rocks  of  Colchester,  so  far  as  seen  by  the  writer,  seem 
to  belong  to  a  common  formation  and  to  be  of  Lower  Cambrian 
age.  No  rocks  were  noted  in  this  township  which  could  be  cor- 
related with  the  limestone  conglomerate,  or  with  other  rocks  which 
have  been  noted  in  northern  townships  that  seemingly  were  not 
so  easily  placed  in  the  Lower  Cambrian  formation ;  but  the  ap- 
parent or  actual  absence  of  such  rocks  may  be  a  circumstance  due 
to  covering,  or  erosion,  or  to  the  particular  nature  of  the  second- 
ary structures  of  the  rocks  of  this  area. 

Essex  Township. 
(Milton   and   Burlington  topographic   sheets.) 

Location.  This  township  adjoins  Colchester  on  the  east. 
It  is  bounded  on  the  north  by  Westford,  on  the  east  by  Jericho, 
and  on  the  south  by  Williston  and  part  of  South  Burlington. 

General  description.  The  rocks  of  Essex  are  the  eastward 
continuation  of  those  of  Colchester  and  the  southward  continua- 
tion of  those  in  Milton  and  Westford. 

In  western  Essex,  north  of  Essex  Junction  and  east  of  the 
road  from  the  Junction  to  Colchester  village,  quartzite  and  dolo- 
mite, apparently  interbedded,  form  the  western  slope  of  hilly  land 
over  which  ascends  the  road  from  School  No.  2  to  Butlers  Cor- 
ners. The  rocks  dip  easterly  and  are  entirely  similar  to  the  rocks 
of  eastern  Colchester.  The  quartzite  is  often  somewhat  mashed 
and  veined  with  quartz.  These  rocks  are  succeeded  along  the 
road  to  Butlers  Corners  by  greenish  slate  or  phyllite.  Slate  was 
traced  to  a  half  mile  east  of  Essex  Center. 

In  the  eastern  part  of  the  township  the  rock  is  prevailingly 
a  quartzitic  schist,  carrying  segregated  quartz,  and  is  the  con- 
tinuation of  similar  rock  south  of  Westford  village.  On  account 
of  shearing,  the  primary  structural  features  of  the  rocks  in  the 
eastern  part  of  the  township  are  obscure. 

Black  quartzitic  schist  outcrops  in  Essex  Junction. 

At  the  bridge  across  the  Winooski,  beneath  the  dam  above 
and  below  the  bridge,  is  gray  siliceous  limestone  or  dolomite, 
often  much  crushed  and  strongly  crystalline.  It  holds  to  a  rather 
uniform  color  and  character  throughout  the  considerable  mass 
exposed.  At  one  place  at  its  western  edge,  below  the  bridge,  the 
jammed  limestone  can  be  seen  resting  on  crumpled  blackish  slate 


REPORT  OP  THE  VERMONT  STATE   GEOLOGIST  225 

on  which  it  has  apparently  been  thrust.  The  ages  of  these  rocks 
are  problematical.  The  limestone  has  been  tentatively  called 
Beekmantown.  It  is  part  of  the  band  called  the  Eolian  Limestone 
in  the  Vermont  Report.  The  descriptions  of  the  members  of  this 
band  have  not  differentiated  among  the  different  kinds  of  rock 
found  in  it.  As  will  appear  in  later  discussions  there  is  much 
variation  and  probably  rocks  of  very  different  ages  are  associated. 
The  structural  relations  are  everywhere  very  obscure. 

Burlington  Township. 

(Plattsburg,  Milton  and  Burlington  topographic  sheets.) 

Location.  Burlington  lies  just  south  of  Colchester.  The 
lake  forms  its  western  boundary  and  it  is  bordered  on  the  east 
and  south  by  South  Burlington. 

The  lake  shore  and  vicinity.  The  northwestern  part  of  the 
township  forms  a  part  of  what  may  be  called  the  Colchester- 
Burlington  peninsula.  In  this  part  the  land  is  low  like  that  of 
the  adjoining  part  of  Colchester,  from  which  it  is  separated  by 
the  Winooski  River.  East  of  this  lowland  is  higher  land  marking 
the  southward  extension  of  the  Red  Sandrock  of  Colchester. 
Northwest  of  Burlington,  at  a  promontory  variously  known  as 
Sharp  Shins,  Spht  Rock  Point,  Lone  Rock  Point,  or  simply  as 
Rock  Point,  the  Sandrock  reaches  the  shore.  At  this  place  it  is 
often  a  yellowish  magnesian  sandstone,  as  weathered.  On  the 
south  side  of  the  point  it  rises  abruptly  from  the  water,  but  north- 
ward on  the  west  it  rests  by  thrust  on  crumpled  Ordovician  slates. 
This  locality  gives  the  finest  thrust  contact  of  the  Red  Sandrock 
on  the  slates  anywhere  to  be  seen  and  has  been  frequently  fully 
described.  The  slickensided  under  surface  of  the  Cambrian  rock 
is  most  impressive. 

From  Rock  Point  southward,  west  and  southwest  of  Bur- 
lington, a  low  sandy  beach  extends  for  a  distance  of  over  three 
miles,  nearly  to  the  blunt  promontory  marked  at  its  southwestern 
extremity  by  Redrock  Point.  This  point  should  not  be  confused 
with  the  one  bearing  the  name  Red  Rock  Point  at  Malletts  Bay. 

From  outcrops  near  Lakeside  Park  to  Queen  City  Park,  the 
rock  along  the  water  edge  is  the  variegated  Sandrock,  but  in 
general  is  distinguished  by  red  or  reddish  colors.  Northward  the 
ledges  are  low  and  permit  one  to  walk  close  to  the  water,  but 
near  and  at  Redrock  Point  are  bold,  precipitous  cliffs.  Ripple 
marks  and  mud  crack  patterns  are  frequent  in  these  rocks  as  at 
other  places  near  Burlington.  The  beds  dip  to  the  east.  These 
red  rocks  may  be  traced  at  the  surface  eastward  through  Red- 
rocks  Park.  No  massive  gray  dolomite  was  noted  in  association 
with  them. 

The  rocks  at  Redrock  Point  undoubtedly  extend  eastward 
beneath  the  surface  deposits  to  join  with  those  at  Willard's  Ledge, 


226  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

now  commonly  known  as  Phelps'  quarry,  a  locality  in  the  south- 
ern outskirts  of  Burlington,  to  the  east  of  the  main  road  from 
Burlington  to  Shelburne.  In  the  quarry  one  has  fine  opportunity 
to  observe  the  variations  in  thickness  and  shades  of  color  from 
bed  to  bed  and  to  see  various  forms  of  markings  due  to  their 
shallow  water  origin.     The  series  is  cut  by  dikes  of  igneous  rock. 

About  a  mile  to  the  east-northeast  of  Phelps'  quarry,  along 
the  road  from  Shelburne  Falls  to  Burlington,  are  low  ledges  of 
gray  sandy  dolomite,  dipping  gently  to  the  east,  which  presumably 
lie  stratigraphically  above  the  beds  of  the  quarry.  This  sandy 
dolomite  is  on  the  meridian  of  gray  dolomite  lying  on  the  red 
beds  at  Winooski  lower  falls,  which  will  presently  be  mentioned. 

Within  the  city  of  Burlington,  outcrops  of  the  Sandrock  are 
few,  but  drilled  wells  in  the  western  part  of  the  city  are  described 
as  penetrating  this  formation  and  there  is  no  doubt  that  the  city 
is  underlain  by  it. 

Gorge  of  the  Winooski.  The  Winooski,  like  the  Lamoille, 
has  cut  post-glacial  gorges  along  its  course  and  the  rocks  so  ex- 
posed, with  some  that  occur  in  Winooski  village  and  to  the  east 
of  it,  may  be  conveniently  described  at  this  point. 

At  the  falls  in  Winooski  village  are  red  beds  much  like  those 
on  the  east  shore  of  Malletts  Bay  and  south  of  Burlington.  Above 
these  red  beds  in  midstream  and  in  the  south  wall  of  the  gorge, 
below  the  bridge,  is  more  or  less  massive-looking  but  obviously 
bedded,  grayish  dolomite.  The  reddish  beds  below  the  gray  rock- 
are  prevailingly  thin,  of  various  shades  of  red  color,  often  brick- 
red,  and  carry  here  and  there  ripple  marks,  mud  cracks  and  some 
cross-bedding.  The  beds  thin  out  and  thicken  laterally  and  have 
all  the  marks  of  shallow  water  deposits. 

Gray  dolomite  outcrops  in  Winooski  village  in  the  railroad 
cuts,  on  the  line  of  strike  of  the  similar  rock  in  the  river  bank 
below  the  bridge.  On  the  south  side  of  the  river,  in  Burlington, 
east  of  the  Greenmount  Cemetery  and  west  of  Grove  Street,  are 
typical  variegated  beds  of  this  formation  dipping  gently  easterly. 

It  will  thus  be  seen  that  along  and  near  the  lake  in  Burling- 
ton the  Red  Sandrock  shows  the  same  general  characters  and 
dip  that  it  has  farther  north  along  the  lake  shore. 

About,  a  mile  east  of  Winooski  village  the  river  has  cut  a 
winding  gorge.  At  the  hydroelectric  power  plant  the  wall  of  the 
gorge  is  made  of  gray  siliceous  rock  which  eastward  appears  to 
pass  beneath  other  rock  that  is  more  calcareous  and  which  in  fact 
at  the  lime-kilns  is  a  marbly  limestone  which  is  quarried  for 
lime.  No  sharp  line  of  separation  was  found  between  the  two 
kinds  of  rock.  In  the  old  and  new  quarries  at  the  lime-kilns  the 
rock  is  strongly  crystalline,  remarkably  uniform  in  appearance 
and  without  distinct  bedding.  A  similar  lack  of  bedding  appears 
in  the  massive,  weathered  rock  as  it  outcrops  near  the  quarry  in 
the  wall  of  the  gorge  just  below  the  bridge.     West  of  the  new 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  227 

quarry,  south  of  the  river,  surface  exposures  in  the  fields  show 
bluish-gray,  marbly  limestone  puddled  with  yellowish-gray  rock. 
The  latter  as  eroded  most  often  appears  as  patches  and  streaks  on 
the  marbly  rock.  The  white-weatheriijg,  marbly  rock  occurs 
north  of  the  river  and  the  railroad  track,  to  the  west  of  the  high- 
way bridge,  and  passes  westward  at  the  surface  into  gray,  siliceous 
rock. 

No  fossils  were  obtained  from  any  of  these  rocks  and  their 
structural  relations  are  problems  not  yet  solved.  In  notable 
particulars  the  limestone  in  the  quarries  and  adjacent  fields  has 
very  strong  resemblance  to  the  similar  rocks  east  of  Highgate 
Springs  and  south  of  Swanton  village. 

Professor  Perkins  has  told  the  writer  that  fossils  were  found 
by  Griffin  in  Colchester,  north  of  the  lime-kilns,  which  seem  to 
be  of  Beekmantown  age  (Rhaphistoma  canadense  Bill,  and  Cryp- 
tosoon  wingi  Seely). 

East  of  the  lime-kilns  the  Winooski  winds  through  a  sand 
plain  to  the  falls  at  the  bridge  south  of  Essex  Junction. 

South  Burlington. 

(Burlington  topographic  sheet.) 

Location.  This  township  bounds  Burlington  on  the  east  and 
south.  For  a  mile  and  a  half  south  of  Redrock  Point  the  shore 
of  Shelburne  Bay  forms  its  western  boundary.  Williston  lies  to 
the  east  and  Shelburne  to  the  south. 

General  description.  The  red  beds  of  the  Sandrock  forma- 
tion pass  beneath  the  surface  covering  near  Queen  City  Park,  and 
the  shore  southward  to  the  southern  boundary  of  the  township 
shows  no  outcrops.  East  of  the  shore,  sand  is  plentiful ;  the 
eastward  extension  of  the  red  beds  in  South  Burlington  may  only 
be  conjectured.  Sand  plains  extend  to  the  northwestern  part  of 
the  township,  to  the  bank  of  the  Winooski  River. 

About  two  and  a  half  miles  southeast  of  Burlington  a  road 
from  the  Williston  turnpike  crosses  Potash  Brook.  At  this  place 
is  white,  marbly  rock  like  that  at  the  lime-kilns  two  miles  to  the 
north. 

Southeast  of  these  outcrops  and  again  southward  along  the 
road  from  Williston  turnpike  to  Hinesburg  and  between  the  road 
and  Muddy  Brook  are  numerous  ledges  of  limestone.  Some  of 
these  are  composed  of  thinly-bedded,  bluish  rock,  of  which  the 
bedded  characters  are  somewhat  better  shown  in  outcrops  a  little 
to  the  east  in  Williston,  and  other  ledges  are  more  massive  looking 
rocks  of  somewhat  striped  appearance  as  though  thin  layers  had 
been  welded  by  shearing  into  more  compact  and  thicker  beds. 
This  massive,  striped  rock  is  particularly  well  shown  at  the  school- 
house  about  two  and  a  half  miles  south  of  the  Williston  turn- 
pike.    The  rocks  were  searched  for  fossils  without  success.    They 


228  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

lie  on  meridians  a  little  east  of  those  occupied  by  the  marbly 
limestone  and  its  associates  at  the  lime-kilns  east  of  Winooski. 
There  is  some  resemblance  between  certain  members  of  the  lime- 
stones near  the  Winooski  gorge  and  those  in  the  southeastern 
part  of  South  Burlington.  The  rocks  at  these  two  places  are 
much  more  readily  correlated  with  each  other  than  either  are  with 
the  gray,  sandy  dolomite  (siliceous  limestone)  found  in  associa- 
tion with  the  red  beds  of  the  Sandrock  formation  at  the  west 
and  that  with  which  they  or  similar  rocks  are  rather  intimately 
intermingled  a  little  farther  south  in  St.  George  and  Hinesburg. 
In  Hinesburg  a4id  Charlotte  and  townships  south  of  them, 
marbly  limestone  is  often  in  intimate  field  association  with  rocks  of 
very  different  character  and  which  may  be  correlated  without  much 
hesitation  with  the  Lower  Cambrian ;  but  these  latter  rocks  are 
quite  similar  in  all  essential  features  to  rocks  which  more  distantly 
surround  the  white,  marbly  or  bluish  limestones  of  South  Bur- 
lington and  Williston.  In  other  words,  there  is  a  rather  close 
correspondence  between  various  rocks  in  South  Burlington  and 
Williston  and  others  in  the  townships  to  the  south  of  them ;  but 
the  field  intimacy  among  these  rocks  that  are  apparently  of  very 
different  age  is  much  more  pronounced  in  some  areas  than  in 
others. 

Williston  Township. 

(Burlington  topographic  sheet.) 

Location.  Williston  lies  east  of  South  Burlington.  It  is 
bounded  'on  the  north  by  Essex,  on  the  east  by  Jericho  and  Rich- 
mond and  on  the  south  by  St.  George  and  a  part  of  Hinesburg. 

General  description.  In  Williston,  along  and  west  of  the 
road  running  south  from  Essex  Junction  to  Hinesburg,  about  one 
and  one-fourth  miles  from  the  outcrops  in  the  river  at  the  bridge 
south  of  Essex  Junction,  Allen  Brook  cuts  through  gray,  siliceous 
limestone  or  dolomite  much  like  that  at  the  bridge. 

The  Hinesburg  road  crosses  the  Williston  turnpike.  One- 
third  of  a  mile  south  of  the  turnpike,  east  of  the  road  to  Hines- 
burg, black,  gray- weathering  slate,  with  easterly  dipping  cleavage, 
is  associated  with  mashed  limestone  or  dolomite,  bluish-gray  on 
fresh  surfaces,  but  weathering  gray,  which  is  very  close  to  the 
slate.  Contact  is  concealed.  The  limestone  showed  no  discern- 
ible dip.  The  relations  are  very  similar  to  those  below  the  bridge 
south  of  Essex  Junction,  described  above. 

About  a  mile  east  of  these  outcrops,  just  south  of  the  Willis- 
ton turnpike,  conspicuous  knolls  give  a  surface  succession  from 
west  to  east  of  siliceous  dolomite,  fissile,  blackish  and  lighter 
colored  phyllites,  and  quartzite.  Gray  dolomite  outcrops  a  mile 
to  the  northeast,  north  of  Allen  Brook ;  but  eastward  the  prevail- 
ing rock  is  quartzitic  schist,  often  carrying  segregated  quartz. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  229 

South  of  Williston  turnpike,  east  of  the  road  running  from 
Essex  Junction  to  Hinesburg,  except  for  the  outcrops  mentioned 
above,  the  prevaiHng  rock  is  the  quartzitic  schist,  which  forms 
rolHng,  hilly  land  extending  eastward  into  Richmond  and  south- 
ward into  St.  George  and  Hinesburg.  This  schist  gives  place  at 
the  surface  westward,  north  of  Brownell  Mt.  and  Sucker  Brook, 
to  bluish  limestone  with  which  the  schist  is  intermingled  at 
places  in  no  regular  way.  The  arrangement  gives  the  impression 
that  the  limestone  lies  on  the  schist.  Westward  toward  Muddy 
Brook  the  limestone  thickens  and  becomes  more  massive  looking, 
as  described  above  for  the  eastern  part  of  South  Burlington,  and 
outcrops  of  schist  are  lacking. 

At  the  foot  of  the  steep  western  slope  of  Brownell  Mt., 
near  the  road  skirting  the  mountain  on  the  west,  is  crushed  bluish- 
black  slate  with  cleavage  dipping  easterly  and  at  some  places 
clearly  brecciated.  The  schist  making  up  the  mass  of  Brownell 
Mt.  has  apparently  ridden  by  thrust  over  the  slate.  West- 
ward the  slate  is  succeeded  by  striped,  bluish  limestone  like  that 
described  above. 

Although  no  conglomerate  was  noted  in  .the  limestones  south 
of  the  Winooski  there  is  much  resemblance  between  the  striped, 
bluish  members  of  them  and  similar  rocks  found  farther  north  in 
the  conglomerate  formation.  There  is,  moreover,  a  close  corre- 
spondence in  the  associations  with  other  rocks  and  in  structural 
relations.  At  the  north  the  rocks  as  has  been  shown  are  often  no 
more  conglomeratic  than  are  the  limestones  of  South  Burlington 
and  Williston. 

Shelburne  and  St.  George  Townships. 

(Willsboro  and  Burlington  topographic  sheets.) 

Location.  Shelburne  lies  south  of  South  Burlington  and 
borders  the  lake.  The  northeastern  part  of  the  township  adjoins 
the  southwestern  part  of  Williston.  St.  George  on  the  east  is 
like  a  small  strip  cut  off  from  the  eastern  end  of  Shelburne.  On 
the  south  are  Charlotte  and  Hinesburg.  A  long  tongue  of  land 
belonging  to  Shelburne  extends  northward  into  the  lake  and 
separates  the  main  body  of  Lake  Champlain  from  Shelburne  Bay. 

General  description.  Most  of  the  peninsula  just  mentioned 
is  formed  of  the  shale  formation  which  extends  from  Shelburne 
Point  southward  on  both  shores,  on  the  east  nearly  to  the  southern 
limit  of  the  bay  and  on  the  west  to  join  the  shale  of  the  mainland 
along  which  it  continues  with  some  interruptions  along  shore  to 
the  southern  boundary  of  the  township.  Outcrops  are  frequent 
on  the  peninsula  between  its  shores,  but  southward  away  from 
the  lake  the  shales  are  mostly  covered  and  are  succeeded  eastward 
by  the  red  and  gray  rocks  of  the  Sandrock  series. 


230  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

On  Shelburne  peninsula  the  shales,  or  slates,  carry  the  firmer, 
rusty-weathering  bands  so  characteristic  of  this  formation  all 
along  the  lake  shore  north  of  Burlington  and  in  general  lithological 
features  are  like  the  members  of  the  formation  on  the  islands 
and  the  mainland  in  the  northern  part  of  the  lake  region. 

It  seems  probable  that  the  lake  bottom  in  Burlington  and 
Shelburne  Bays  is  underlain  by  the  slates,  in  which  these  indenta- 
tions of  the  shore  have  been  excavated,  probably  in  some  cases 
after  a  covering  of  overthrust  rock  belonging  to  older  limestones 
or  to  the  Sandrock  series  had  been  eroded.  The  general  field  re- 
lations all  about  suggest  such  a  history  and  further  give  some 
support  to  the  view  that  in  Shelburne  and  other  places  where 
these  friable  mud  rocks  have  been  preserved  they  owe  their  pres- 
ervation to  a  covering  of  more  resistant  rock  that  was  removed 
at  a  relatively  recent  date.  Juniper  and  White  Islands  are  in- 
sular outcrops  of  the  shale  to  the  west  of  the  peninsula. 

The  slates  on  Shelburne  peninsula  are  cut  by  numerous  dikes 
which  have  been  described  by  Kemp.^ 

The  Sandrock  forms  headlands  on  the  southwest  shore  of 
Shelburne  Bay  and  gives  numerous  outcrops  between  the  bay  and 
the  village  of  Shelburne.  The  red  beds  are  conspicuous  along 
the  Shelburne-Burlington  road  just  north  of  the  LaPlatte  River 
and  these  and  other  members  outcrop  west  and  southwest  of 
Shelburne  village.     The  dip  is  at  a  low  angle  to  the  east. 

East  of  Shelburne  Falls,  to  Shelburne  Pond,  the  rocks  are 
gray,  siliceous  dolomites  not  distinguishable  from  the  similar  beds 
around  Shelburne  village.  The  rocks  just  east  of  Shelburne  Falls 
are  on  the  meridian  of  those  in  the  eastern  part  of  Burlington. 

East  of  Shelburne  Pond,  between  it  and  the  main  road  from 
Burlington  to  Hinesburg,  the  prevailing  rocks  are  marbly  or 
bluish  limestones,  forming  the  southward  continuation  of  those 
in  the  southwestern  part  of  Williston  and  the  southeastern  part 
of  South  Burlington.  Near  the  Hinesburg  road  these  limestones 
give  place  to  gray,  siliceous  dolomite  which  continues  over  the 
western  boundary  of  St.  George  township.  East  of  the  dolomite 
in  St.  George  the  hilly  land  is  made  of  quartzitic  schist  which 
joins  that  of  Williston  and  Hinesburg. 

A  generalized  surface  section  from  west  to  east  across  the 
areas  south  of  the  Winooski  River,  which  have  so  far  been  de- 
scribed, gives  the  Ordovician  shale  formation  at  the  west,  then 
the  Red  Sandrock  series  of  red  and  gray  quartzites  and  dolomites, 
then  a  very  different  kind  of  rock  that  is  a  metamorphosed  lime- 
stone, and  finally  quartzitic  schist  with  some  gray  dolomite  on 
the  same  meridians  with  the  schist  both  of  which  belong  to  the 
same  general  formation.  The  types  of  rock  and  the  sequence  are 
the  same  as  in  the  townships  north  of  the  Winooski.     The  varia- 

'Bull.  U.  S.  G.  S..  No.  107,  1893. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  231 

« 

tions  are  perhaps  less  significant  than  the  similarities,   from  a 
structural  viewpoint. 

Charlotte  Township. 

(Willsboro  and  Burlington  topographic  sheets.) 

Location.  Charlotte  lies  south  of  Shelburne  and  borders  the 
lake.  It  is  bordered  by  Monkton  on  the  east  and  by  Monkton  and 
Ferrisburg  on  the  south. 

The  rocks  along  and  near  the  lake  in  Charlotte.  From  the 
Shelburne  line  to  the  latitude  of  Wing's  Point  the  lowland  along 
the  lake  is  made  of  clay,  with  few  outcrop's  of  the  shales  along 
shore. 

On  the  road  running  from  Charlotte  village  westward  to  the 
lake  shore  and  McNeil's  ferry,  about  a  mile  east  of  the  shore, 
Black  River  limestone,  carrying  the  markings  so  familiar  in  this 
formation  in  the  lake  region,  dips  westerly  at  a  low  angle  and  is 
underlain  apparently  by  Upper  Chazy  with  similar  westerly  dip. 
Nearer  the  lake  are  Trenton  beds,  also  dipping  westerly  at  a  low 
angle  or  lying  nearly  flat.  At  the  water  edge  just  south  of  the 
ferry  the  dark  blue  Trenton  rocks  are  full  of  well-preserved  and 
characteristic  basal  Trenton  fossils.  After  a  surface  interruption 
along  the  shore  of  the  bay  south  of  the  ferry  the  Trenton  beds 
appear  on  the  north  shore  of  Cedar  Beach  promontory  and  con- 
tinue around  its  border  to  McNeil  Bay.  At  Cedar  Beach  prom- 
ontory the  dip  changes  to  southeast  or  east.  These  Trenton 
rocks  are  nowhere  severely  altered.  They  are  in  fact  like  the 
Trenton  rocks  of  Grand  Isle  and  Isle  La  Motte.  In  respect  to 
certain  features  of  alteration  they  dififer  from  the  Chazy  just  as  do 
the  beds  on  the  islands  mentioned. 

On  the  west  shore  of  a  small  promontory  that  juts  into 
McNeil  Bay  are  beds  that  were  correlated  with  part  of  Brainerd 
and  Seely's  Beekmantown.  A  third  of  a  mile  farther  east  are 
magnesian  rocks  of  doubtful  correlation,  but  probably  also  Beek- 
mantown. These  are  followed  eastward  by  ledges  of  Chazy  lime- 
stone, dipping  easterly,  and  carrying  Girvanella  ocellata  Seely. 
There  seems  to  be  exposed  a  small  patch  of  Black  River  to  the 
east  of  these  Chazy  rocks. 

The  road  on  Thompson's  Point  crosses  diagonally  a  series 
of  beds  that  appear  to  belong  to  the  Beekmantown  by  comparison 
with  the  Shoreham  section.  The  beds  dip  at  a  low  angle  to  the 
southeast. 

On  the  southeast  shore  of  the  bay,  south  of  Thompson's  Point 
near  the  Ferrisburg  line,  are  Chazy  beds  dipping  to  the  southeast. 

The  various  massive  beds  described  as  probably  Beekman- 
town or  recognizable  as  Chazy,  are  not  folded,  but  as  shown  by 
changes  in  strike  from  place  to  place  and  by  visible  geographic 
offsets  are  twisted,  and  broken  across  the  strike  and  probably 


232  REPORT  OP  THE  VERMONT  STATE  GEXDLOGIST. 

along  it.  On  the  whole  the  rocks  do  not  show  pronounced  in- 
dications of  internal  deformation.  There  is  nothing  to  show  their 
relations  to  the  slates  that  probably  lie  north  of  them  under  the 
clay-covered  lowland.  The  writer's  field  map  indicates  that  shale 
lies  on  a  meridian  to  the  east  of  these  massive,  basal  Ordovician 
rocks ;  outcrops  were  noted  a  mile  north  of  Charlotte  station  and 
also  a  few  rods  west  of  Ferrisburg  station  in  the  adjoining  town 
of  Ferrisburg.  These  various  rocks  in  southwestern  Charlotte 
belong  to  the  lake  region  proper,  as  defined  in  the  early  part  of  this 
paper.  The  probable  relations  among  them  may  be  judged  from 
those  shown  by  other  rocks  in  townships  farther  south. 

East  of  the  Rutland  railroad  track  in  Charlotte.  South  of 
Charlotte  station  is  a  considerable  mass  of  igneous  rock  forming 
Barber  Hill.  The  rock  has  been  described  as  Bostonite  (a  soda- 
rich,  acid,  dike-forming  rock).  Similar  rock  forms  dikes  on 
Shelburne  Point  and  in  North  Ferrisburg  village. 

East  of  the  railroad  track  in  Charlotte  township  by  far  the 
largest  part  of  the  visible  rock  emerging  through  the  drift  belongs 
to  the  Sandrock  series.  East  of  Charlotte  village  the  reddish 
members  of  this  formation  form  Pease  Mt.  Along  the  road  that 
runs  southward,  east  of  Pease  Mt.,  similar  rocks  dip  easterly  and 
join  with  the  red  beds  of  Mt.  Philo.  The  rocks  of  these  two 
mountains  are  on  meridians  which  are  occupied  farther  north  by 
the  Sandrock  formation  in  Shelburne,  but  which  to  the  south  in 
Ferrisburg  are  occupied  by  comparatively  unaltered  shales,  thinly- 
bedded,  dark  blue,  basal  Trenton  limestone  and  Chazy  rocks 
which  belong  to  the  lake  series  and  are  in  fact  the  eastward  ex- 
tension of  the  rocks  along  the  lake  in  Ferrisburg. 

East  of  Pease  Mt.,  around  East  Charlotte,  exposed  at  sev- 
eral places  along  or  near  the  road  running  in  a  north-south 
direction  through  the  village,  are  outcrops  of  beds  of  siliceous 
dolomite,  dipping  easterly  at  a  low  angle.  On  this  road,  about  a 
mile  and  a  fourth  north  of  the  village,  is  marbly  limestone ;  but  a 
mile  farther  north  the  gray  dolomite  outcrops  again  and  continues 
towards  Shelburne  Falls. 

Around  Prindle  Corners,  two  miles  southeast  of  East  Char- 
lotte, interbedded  quartzite  and  dolomite  show  a  series  much  like 
that  found  around  Middlebury  and  Brandon  to  the  south.  The 
rocks  in  southeastern  Charlotte  and  adjacent  portions  of  Hinesburg 
indeed  mark  a  transition  in  the  Lower  Cambrian  formation  from 
the  generally  more  massive,  interbedded,  siliceous  and  magnesian 
rocks  of  the  Sandrock  series  in  the  northern  townships  and  the 
recognizably  thinner  beds  of  what  has  been  called  by  the  writer 
in  earlier  papers  the  "interbedded  series"  of  the  Lower  Cambrian 
in  the  Vermont  valley. 

As  a  consequence  of  their  more  thinly-bedded  character,  the 
rocks  around  Prindle  Corners  and  neighboring  parts  of  Hines- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  233 

burg  are   frequently  jammed  into  close   folds  so  that  the  beds 
stand  at  high  angle  of  dip  or  even  on  end. 

Northeast  of  Prindle  Corners  along  the  road  and  in  the 
fields  the  Cambrian  quartzites  and  dolomites  are  intermingled 
with  marbly  rock,  but  the  field  relations  as  usual  give  no  definite 
clues  as  to  the  structural  relations. 

Hinesburg-  Township. 

(Burlington  topographic  sheet.) 

Location.     Hinesburg  lies  east  of  Charlotte. 

General  description.  In  the  southwestern  part  of  Hinesburg 
are  interbedded  quartzites  and  dolomites  which  join  with  those 
around  Prindle  Corners  in  southeastern  Charlotte.  The  beds  are 
usually  sharply  folded  with  high  easterly  or  westerly  dips,  but 
along  the  meridians  of  such  closely  folded  rocks,  at  other  places 
the  folding  was  not  always  so  severe.  The  interbedded  rocks 
east  of  Prindle  Corners  continue  southward  into  Monkton  and 
northward  in  western  Hinesburg,  but  in  northwestern  Hinesburg 
are  considerable  exposures  of  marbly  limestone,  which,  so  far  as 
the  hard  rock  is  now  visible,  seem  more  or  less  definitely  to  be 
surrounded  by  gray,  siliceous  dolomites. 

West  of  Mechanicsville,  along  and  west  and  east  of  the 
Hinesburg  road,  the  gray  dolomite  is  abundant  and  forms  a  con- 
spicuous ledge  known  as  High  Rock  on  the  east  side  of  the  road. 
Massive,  gray  dolomite  occurs  between  Mechanicsville  and  Hines- 
burg and  in  numerous  massive  and  prominent  ledges  southeast  of 
Hinesburg  on  the  east  side  of  the  road  to  Starksboro,  continuing 
southward  nearly  to  the  township  boundary.  The  extension  of  the 
dolomite  east  of  the  main  road  is  irregular,  being  most  marked  in 
hollows  around  Mechanicsville  and  Hinesburg.  East  of  the  main 
road  the  land  is  mostly  hilly  and  made  of  quartzitic  schist. 
Dolomite  and  schist  at  different  places  occupy  the  same  meridians 
and  the  field  relations  show  that  the  two  rocks  are  members  of  a 
common  formation  and  that  the  preservation  of  the  dolomite 
along  the  western  margin  of  the  hilly  land  is  due  to  certain  favor- 
able structural  relations  resulting  from  the  deformation  of  the 
rocks. 

It  will  thus  be  seen  that  from  the  lake  shore  eastward  through 
Charlotte  and  Hinesburg  a  broad  surface  section  gives  near  the 
lake  the  shales  and  comparatively  unaltered  limestones  of  clearly 
recognizable  Lower  and  Middle  Ordovician  ages,  then  an  abrupt 
transition  to  the  Red  Sandrock  of  Pease  Mt.  and  Mt.  Philo 
which  are  succeeded  eastward  by  gray  dolomites  and  interbedded 
dolomites  and  quartzites  more  or  less  intimately  intermingled  in 
their  present  .surf ace  outcrops  with  marbly  limestone,  and  finally 
the  massive,  gray  dolomite  and  quartzitic  schist  of  the  hilly  land 
at  the  east.     A  field  inspection  is  essential  in  order  to  appreciate 


234  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

fully  the  similarity  which  such  a  section  has  in  rock  types, 
sequence  and  general  field  relations  with  the  sections  in  northern 
townships  which  have  been  described,  and  its  correspondence  in  all 
essential  particulars  with  areas  farther  south.  These  resem- 
blances are  clearly  due  to  what  may  be  called  strict  homology,  to 
borrow  a  biological  term,  in  the  secondary  structural  features  and 
in  certain  primary  relations  which  obtained  among  the  various 
rocks,  although  all  of  the  rocks  may  not  be  of  precisely  similar 
age. 

The  Lower  Cambrian  formation  is  seen  to  show  from  west 
to  east  and  from  north  to  south  many  variations  of  thickness, 
color  and  sequence  in  the  vertical  arrangement  of  its  beds,  cor- 
respondifig  with  lateral  variations  in  the  original  character  of  the 
material  and  variations  in  the  conditions  under  which  the  material 
was  deposited  from  time  to  time.  North  of  Weybridge  the  more 
purely  terrigenous  rocks  of  this  formation  are  found  in  the  hilly 
land  by  which  the  Champlain  lowland  is  joined  to  the  mountains 
farther  east,  but  such  rocks  also  form  the  present  surface  rock 
over  portions  of  the  eastern  edge  of  the  lowland.  South  of  Wey- 
bridge the  terrigenous  rocks  are  extensively  preserved  in  the 
Taconic  hills. 

ADDISON  COUNTY. 

Ferrisbnrg  and   Vergennes. 

(Willsboro,  Burlington,  Port  Henry  and  Middlebury  topographic 

sheets.) 

Location.  The  township  of  Ferrisburg  and  the  city  of  Ver- 
gennes are  conveniently  discussed  together.  Ferrisburg  is  on  the 
lake  shore  south  of  Charlotte.  On  the  east  it  adjoins  Monkton 
and  part  of  New  Haven  and  on  the  south  is  bounded  by  part  of 
New  Haven,  Waltham,  Vergennes  and  Panton.  Vergennes  forms 
an  area  two  miles  square  which  is  bounded  by  Ferrisburg  on  the 
north,  by  Ferrisburg  and  Waltham  on  the  east,  by  Waltham  and 
Panton  on  the  south  and  by  Panton  and  Ferrisburg  on  the  west. 

General  description.  Ferrisburg  is  a  large  township  and 
includes  a  variety  of  rocks,  all  of  which  ma:y  be  correlated  with 
others  which  have  been  described  in  previous  pages,  but  some  of 
which  show  field  relations  of  great  interest  in  relation  to  the 
general  structure  of  the  region.  Description  will  begin  with  the 
western  and  central  portions. 

Around  Camp  Meeting  Point,  north  of  the  mouth  of  Lewis 
Creek,  fossiliferous  Chazy  limestone  forms  a  low,  anticlinal  fold. 
Between  the  point  and  the  railroad  track  are  low  outcrops  of 
shales  which  are  undoubtedly  younger  than  the  rock  at  the  point. 

Near  Bluff  Point,  west  of  the  Little  Otter,  much  of  the 
rock  is  apparently  of  Chazy  age.     Specimens  of  Maclurea  magna 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  235 

were  found  near  the  road  from  Kingsland  Bay  to  Ferrisburg,  at 
the  bend  in  the  road,  about  two-thirds  of  a  mile  east  of  the  bay. 
The  beds  dip  gently  eastward.  East  of  this  place  outcrops  are 
largely  concealed  along  the  sluggish  creek. 

Limestone  outcrops  at  intervals  along  the  road  that  runs 
south  from  Kingsland  Bay.  Just  south  of  the  junction  of  this 
road  with  the  one  that  runs  from  it  to  Fort  Cassin  Point  are 
extensive  outcrops  of  probably  Chazy  limestone,  dipping  easterly ; 
but  about  one-fourth  of  a  mile  from  the  main  road  along  the  one 
to  Fort  Cassin  Point,  graptolitic  shales  were  noted.  At  Fort 
Cassin  Point,  which  is  probably  really  an  island  surrounded  partly 
by  water  and  partly  by  the  delta  and  levee  deposits  of  Otter 
Creek,  are  limestones  which  were  assigned  by  Brainerd  and  Seely 
to  division  D  of  their  Beekmantown  formation.  Bedding  is  dis- 
tinct and  the  layers  have  a  flattish  position.  The  rocks  are  more 
or  less  indurated  but  fossiliferous.  Although  great  numbers  of 
different  species  have  been  found  at  this  locality,  particularly  in 
the  weathered  rock,  fossils  are  now  found  only  after  dihgent 
search  in  the  firm,  unweathered  rock.  Seely  states  that  the  Fort 
Cassin  rocks  were  assigned  to  division  D  by  Brainerd  after  care- 
ful stratigraphic  study  of  the  region.  The  fauna  of  these  rocks 
is  in  need  of  further  careful  study  in  order  to  be  sure  of  its  exact 
horizon.  The  apparent  separation  at  the  surface  by  shales  of  the 
rocks  at  Fort  Cassin  from  the  Chazy  beds  mentioned  as  occurring 
along  the  road  to  Kingsland  Bay  suggests  that  the  succession 
east  from  the  lake  is  probably  not  a  conformable  one,  but  rather 
that  breaks,  probably  of  the  nature  of  thrusts,  intervene. 

East  of  the  probable  Chazy  rocks  on  the  Kingsland  Bay  road 
the  surface  is  all  clay.  The  hard  rock  underlying  the  clay  is 
probably  all  shale. 

West  of  Otter  Creek  and  south  of  Kellogg  Bay,  are  outcrops 
of  fossiliferous  Chazy  which  lie  on  a  meridian  slightly  to  the  west 
of  the  Fort  Cassin  beds  a  mile  to  the  north.  With  some  inter- 
ruptions the  Chazy  beds,  dipping  everywhere  to  the  east,  form 
the  shore  and  slopes  adjacent  to  it  from  Summer  Point  at  Kellogg 
Bay  southward  past  Basin  Harbor  to  Button  Bay.  At  many 
places,  notably  at  Basin  Harbor  and  between  it  and  Button  Bay, 
the  beds  afforded  excellent  specimens  of  M.  magna  and  Girvanella. 
Near  Kellogg  Bay  perhaps  not  all  the  rock  belongs  to  the  Middle 
Chazy ;  at  Summer  Point  the  beds  may  belong  to  a  lower  division 
of  this  formation  or  to  Upper  Beekmantown. 

Eastward  again  between  the  outcrops  along  shore  and  Otter 
and  Dead  Creeks,  presumably  the  underlying  rock  is  shale,  which 
is  found  in  scanty,  low  outcrops  along  the  road  from  Basin 
Harbor  to  Panton ;  but  sand  plains  along  the  Otter  and  elsewhere 
clay  conceal  the  rock  to  within  a  mile  and  a  half  of  the  city  of 
Vergennes. 


236  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

The  Chazy  rocks  that  form  the  point  which  projects  towards 
Button  Island,  near  Button  Bay,  pass  eastward  beneath  clay 
which  forms  most  of  the  shore  of  Button  Bay.  Along  the  shore 
south  of  the  bay  the  shales  outcrop  for  a  distance  of  about  two- 
thirds  of  a  mile  north  of  the  Panton  line.  Fossils  collected  from 
these  shales  and  those  along  the  Panton  shore  southward  by 
Gould  and  Ruedemann  were  assigned  by  Ruedemann  to  three 
different  horizons  in  the  Canajoharie  shale  of  Trenton  age. 

About  one  and  a  half  miles  west  of  Vergennes,  north  of  the 
Otter  and  between  it  and  the  road  running  from  Vergennes  to 
Fort  Cassin  and  Kingsland  Bay  is  a  hill  of  badly  crushed,  magne- 
sian  limestone,  without  fossils  or  distinct  structure.  A  mile  to 
the  east,  north  of  the  road,  and  just  west  of  the  playgrounds  of 
the  Industrial  School  are  excellent  outcrops  of  massive  Chazy 
beds,  dipping  gently  to  the  east  and  carrying  numerous  coils  and 
opercula  of  M.  magna  and  abundant  specimens  of  Girvanella. 
East  of  the  playgrounds  and  north  of  the  city,  similar  beds  with 
similar  fossils  dip  to  the  west  at  an  angle  of  34°  and  strike  N. 
40°  E.  East  of  these  outcrops,  west  of  the  railroad  track,  is  a 
road  running  north  to  Ferrisburg.  East  of  this  road,  respectively 
a  half  mile  and  a  mile  north  of  the  westerly-dipping  Chazy  beds 
just  mentioned,  are  other  Chazy  beds  dipping  easterly.  The 
structure  thus  shown  by  the  Chazy  northwest  and  north  of  Ver- 
gennes shows  the  formation  to  be  disposed  in  gentle  anticlinal  and 
synclinal  swells.  More  altered  rocks  of  probably  Chazy  age  at 
Marsh  Hill  and  south  of  it,  to  the  northeast  of  the  city,  form  a 
gentle,  anticlinal  fold. 

At  Vergennes  falls  the  river  tumbles  over  massive,  grayish, 
magnesian  limestone  which  apparently  dips  easterly.  Close  in- 
spection shows  it  to  be  crushed  and  brecciated,  but  now  healed 
into  a  compact  rock.     Seely  called  this  rock  Beekmantown. 

Below  the  falls,  near  the  boat  landing  on  the  Industrial  School 
grounds,  shales  carrying  numerous  graptolites,  identified  as  G. 
quadrimucronatus,  outcrop  in  the  low  bank  of  the  stream.  Be- 
tween the  falls  and  the  westerly-dipping  Chazy  beds  north  of  the 
city,  described  above,  shales  or  argillaceous  limestones,  usually 
much  sheared  and  slickensided  and  filled  with  small  veins  of 
calcite,  outcrop  along  the  road,  apparently  exposed  from  beneath 
a  mass  of  overthrust  Chazy. 

About  two  miles  northeast  of  Vergennes,  west  and  east  of 
the  main  road  from  Vergennes  to  Ferrisburg,  east  of  the  railroad 
track,  are  Trenton  beds  somewhat  sheared,  but  carrying  hosts  of 
recognizable  basal,  Trenton  fossils,  including  Calymene  scnaria, 
Cryptolithus  tesselatus,  linguloid  forms  and  bryozoa.  These 
rocks  are  particularly  well  exposed  on  the  land  of  Carl  Fields. 
The  Trenton  rocks  form  a  ridge  between  the  main  road  and  the 
one  running  from  it  to  the  west  of  Shellhouse  Mt. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  237 

A  half  mile  northeast  of  this  ridge  of  fossiliferotis  Trenton, 
southeast  and  east  of  Ferrisbiirg  village,  are  outcrops  of  Chazy 
limestone  which  are  on  meridians  on  which  lie  the  rocks  at  Marsh 
Hill  and  south  of  it,  as  mentioned  above.  Rocks  of  apparently 
Chazy  age  continue  northward,  east  and  west  of  the  road  on  the 
west  of  Shellhouse  Mt.  North  of  the  mountain  the  road  ascends 
over  blue,  Trenton  rocks,  which  as  outcropping  in  the  road  gave 
Trenton  fossils,  including  C.  tesselatus.  Towards  Mt.  Fuller 
these  Trenton  beds  are  associated  with  more  massive,  dense  lime- 
stones, weathering  a  light  gray,  now  shattered  and  filled  with 
calcite  veins  and  which  strongly  suggest  the  Black  River,  and  are 
in  fact  much  like  recognizable  Black  River  rocks  found  farther 
south  in  Waltham  and  Addison  townships.  Sheared  limestone, 
probably  of  Trenton  age,  continues  northward  along  the  cross 
road  west  of  Mt.  Fuller  nearly  to  the  North  Ferrisburg-Monkton 
road.  At  one  place  along  this  cross  road,  sheared  limestone  is 
in  contact  with  quartzite  and  probably  overlain  by  it.  One-third 
of  a  mile  to  the  east  is  a  scarp  in  the  quartzite  that  makes  Mt. 
Fuller. 

At  North  Ferrisburg  village,  Lewis  Creek  has  cut  down  into 
crumpled,  black  shales  or  shaly  limestones  which  are  exposed  in 
the  bed  and  banks  of  the  stream  at  many  points  in  the  village  and 
west  of  it  towards  the  lake.  Northward  on  the  meridians  of 
these  shales  in  the  creek  is  the  Red  Sandrock  of  Mt.  Philo.  These 
shales  have  been  called  "Utica";  they  are  without  much  doubt 
younger  than  the  rocks  that  form  the  hilly  land  south  and  south- 
east of  them. 

The  rocks  that  apparently  belong  to  the  Chazy  formation 
and  form  the  surface  just  west  of  Shellhouse  Mt.  give  place 
in  the  steep  western  face  of  the  mountain  to  white  quartzite 
which  is  notably  jammed.  The  quartzite  extends  eastward,  giving 
place  near  the  township  boundary  to  interbedded  dolomites  and 
quartzites,  all,  including  the  quartzite  at  Shellhouse  Mt.,  dip- 
ping easterly  at  a  low  angle.  The  interbedded  rocks  form  a 
band  along  the  eastern  edge  of  the  township  and  southward  join 
with  similar  rocks  in  New  Haven.  South  of  Shellhouse  Mt. 
the  Cambrian  rocks  pass  under  drift  and  between  the  band 
of  interbedded  rocks  at  the  east  and  the  limestone  of  Marsh  Hill 
and  neighboring  exposures  is  an  area  of  low,  flat  land,  with  no 
outcrops ;  but  directly  north  of  the  mountain,  as  has  been  shown, 
are  limestones  and  shales  of  the  lake  series  which  occupy  the 
meridians  of  the  quartzite  of  the  mountain  and  the  interbedded, 
Lower  Cambrian  rocks  that  lie  east  of  it. 

The  Trenton  and  Black  River  limestones  southeast  of  North 
Ferrisburg  village  and  the  shales  in  Lewis  Creek  are  visibly 
sheared  or  shattered  rocks  and  somewhat  metamorphosed,  but 
are  readily  recognized  and  traced  as  the  eastward  extension  of 
the  rocks  near  the  lake.     They  are  notably  less  crystalline  and 


238  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

marbly  than  the  calcareous  rocks  found  among  the  Lower  Cam- 
brian rocks  on  meridians  farther  east.  The  occurrence  of  the 
Lower  Cambrian  rocks  north  and  south  of  North  Ferrisburg 
village  on  the  same  meridians  with  the  little  altered  lake  rocks 
near  the  village  and  the  extension  of  the  present  margin  of  the 
former  at  Pease  Mt.  in  Charlotte  to  a  meridian  over  a  mile  west 
of  that  passing  through  North  Ferrisburg  village,  point  to  thrusts 
by  which  the  older  rocks  rode  over  the  younger.  It  is  also 
probable  that  the  massive  limestones  of  the  lake  series  rode  over 
younger  shales,  either  by  independent  thrusts  or  during  the  trans- 
lation of  the  Cambrian  beds. 

The  field  relations  near  Vergennes  certainly  suggest  that  the 
older  limestones  of  the  lake  series  have  ridden  over  the  younger 
limestones  and  shales.  The  latter  are  sometimes  sheared  and 
crushed.  At  Vergennes  falls  the  dolomite  is  brecciated ;  but  the 
Chazy  beds  northwest,  north  and  northeast  of  the  city  are  not 
folded  much.  They  are  most  sheared  and  altered  in  their  eastern 
outcrops ;  but  even  then  may  sometimes  lie  flat,  as  may  be  seen 
near  the  cemetery  east  of  Ferrisburg  village. 

The  conditions  around  Vergennes  seem  to  show  what  was 
argued  to  be  the  probable  structure  on  the  islands  in  the  northern 
part  of  the  lake.  They  also  give  support  to  the  idea  that  a  great, 
low-angle  thrust  carried  the 'Lower  Cambrian  beds  over  the  rocks 
of  the  lake  region  and  that  to  some  extent,  at  least,  the  present 
western  margin  of  the  former  is  an  erosion  trace  of  an  overthrust 
mass  of  which  some  portions  have  disappeared. 

Monkton  Township. 

(Burlington  and  Middlebury  topographic  sheets.) 

Location.  Monkton  lies  east  of  Ferrisburg  and  is  bounded 
by  Charlotte  and  Hinesburg  on  the  north,  by  Starksboro  on  the 
east,  and  by  Bristol  and  part  of  New  Haven  on  the  south. 

General  description.  This  township  includes  a  prominent 
physiographic  outlier  of  the  Green  Mountain  plateau,  generally 
known  as  "Monkton  ridge,"  which  enters  Monkton  from  Bristol 
at  the  south  and  extends  through  the  central  portion  nearly  across 
the  township.  To  the  east  of  Monkton  ridge,  and  separated  from 
it  by  a  valley  of  irregular  surface,  another  prominent  ridge, 
known  as  Hogback  Mt.,  and  which  is  also  an  outlier  of  the  main 
range,  enters  from  Bristol  and  extends  northward  just  west  of 
the  eastern  boundary  to  within  about  a  mile  of  the  northern  town- 
ship line. 

These  prominent  physiographic  features  are  fundamentally  of 
structural  origin.  They  are  interpreted  as  primarily  thrusted 
masses  which  were  later  modified  by  normal  faulting.  The  de- 
pression which  now  separates  Monkton  ridge  from  Hogback  and 
that  which  separates  the  latter  from  the  main  range  is  in  each  case 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST,  239 

a  more  or  less  perfectly  developed  grahen  and  on  a  small  scale 
illustrates  the  structural  character  of  the  famous  Vermont  valley, 
which  beginning  farther  south  near  Brandon  extends  to  Pownal 
between  the  Green  Mountain  plateau  and  the  Taconic  range.  The 
structural  and  physiographic  features  in  the  eastern  part  of  Monk- 
ton  and  adjoining  parts  of  Starksboro  have  their  counterparts  at 
other  places  along  the  western  edge  of  the  Green  Mountain 
plateau. 

Into  the  northwestern  part  of  Monkton  township  the  reddish 
beds  of  the  Sandrock  series  extend  from  the  southeastern  part  of 
Charlotte  and  give  conspicuous  outcrops  on  the  low  hillsides  at 
many  places.  East  of  the  road  from  Monkton  to  East  Charlotte, 
northeast  of  Mt.  Fuller,  the  red  beds  are  interbedded  with  some 
dolomite  and  the  dip  is  gently  to  the  west. 

At  Mt.  Fuller  and  southward  along  the  road  to  Barnumtown, 
beds  of  cherry-red  quartzite  form  conspicuous  outcrops  and  dip 
to  the  east  at  a  low  angle.  A  low  scarp  bounds  Mt.  Fuller  on  the 
west.  It  is  interpreted,  as  in  some  degree  a  recession  scarp,  for 
one-third  of  a  mile  to  the  west  of  it  a  fragmentary  patch  of 
quartzite  rests  against  sheared,  probably  Trenton  limestone,  as 
noted  above. 

South  of  Mt.  Fuller  the  surface  falls  off  to  slightly  lower 
levels  and  apparently  the  purple  quartzites  pass  under  somewhat 
higher  members  of  the  Sandrock  series ;  but  whether  this  is 
actually  the  case  or  whether  the  interbedded  quartzites  and  dolo- 
mites forming  the  surface  rocks  southward  represent  lateral 
variations  of  the  beds  at  the  north  may  not  be  easily  decided. 

Near  Barnumtown  the  interbedded  series  appears  in  force 
and  at  places  shows  most  severe  effects  of  compression,  being 
not  only  jammed  into  close  folds,  but  twisted  along  the  strike  and 
otherwise  deformed.  The  interbedded  rocks  continue  south  from 
Barnumtown  over  Cronkhite  Hill  and  along  the  road  to  New 
Haven  Junction.  At  some  places  the  members  of  this  series  lie 
in  flat  attitude,  but  within  short  distances  such  beds  pass  ap- 
parently both  along  and  across  the  strike  into  others  that  are 
highly  inclined  and  greatly  jammed.  These  features  have  much 
resemblance  to  others  which  have  been  described  for  quite  similar 
rocks  around  Brandon  (see  first  paper)  and  have  their  counter- 
parts in  other  localities  yet  to  be  described. 

In  the  northern  part  of  th'e  township,  along  the  road  from 
North  Ferrisburg  to  the  village  of  Monkton  Ridge,  are  low-lying 
outcrops  of  closely- folded,  interbedded  quartzites  and  dolomites 
which  are  the  southward  extension  of  those  in  southwestern 
Hinesburg  and  near  Prindle  Corners  in  Charlotte. 

Two  miles  farther  south,  just  west  of  Monkton  village 
(Monkton  Borough),  similar  rocks  with  cherry-red  quartzite  mem- 
bers form  the  hill  known  as  Mt.  Florence  and  show  numerous 
outcrops  in  the  fields  directly  north  of  the  hills.     In  the  hill  red 


240  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

quartzites  apparently  dip  gently  to  the  west,  while  directly  east  of 
the  hill  the  members  of  the  interbedded  series  are  jammed  into 
close  folds  and  are  sheared  and  crushed. 

From  Monkton  Borough,  over  the  ridge  to  East  Monkton,  the 
rock  is  mainly  quartzite  or  quartzitic  schist,  apparently  for  the 
most  part  dipping  easterly.  Just  north  of  East  Monkton  village 
rather  thinly-bedded,  quartzite  beds  stand  on  end  or  by  apparent 
overturn  now  dip  easterly  at  a  high  angle.  These  rocks  are  sheared 
and  slickensided  and  give  every  indication  of  having  been  jammed 
against  the  beds  that  lie  west  of  them. 

Distinct  scarps,  irregularly  disposed  and  overlapping  more 
or  less  along  the  general  strike  of  the  rocks,  are  distinctly  visible 
features  along  the  eastern  face  of  the  ridge  north  of  East  Monk- 
ton  village.  These  scarps  probably  mark  planes  of  faulting  by 
which  the  rocks  that  lie  in  the  valley  of  Pond  Brook  have  been 
left  at  lower  levels.  Quartzite  forms  the  eastern  slopes  and 
scarps  of  Monkton  ridge  from  East  Monkton  to  Monkton  Ridge 
village.  South  of  the  latter  village,  east  of  Monkton  Pond,  the 
gray  and  white  quartzite  is  distinctly  sheared  so  that  the  dip  is 
obscure. 

For  a  mile  and  a  half  east  of  Monkton  Ridge  village  the 
rocks  are  distinctly  bedded,  gray  dolomites,  lying  flat  or  dipping 
westerly,  but  just  west  of  the  northern  end  of  Hogback  Mt.  * 
the  dip  of  the  dolomite  changes  to  easterly  and  this  rock  gives 
place  eastward  to  quartzitic  schist,  or  sheared  quartzite,  with 
some  members  of  pure  white,  granular  quartzite.  Eastward 
towards  the  road  that  runs  from  Hinesburg  to  Starksboro  the 
quartzite  gives  place  to  gray,  siliceous  dolomite,  usually  of  massive 
appearance,  but  carrying  some  thin  beds. 

In  Monkton  township,  just  as  in  Hinesburg  at  the  north,  as 
one  goes  east  from  the  western  margin  of  the  Cambrian  rocks 
towards  the  hilly  land,  the  interbedded  rocks  are  seen  to  give 
place  at  the  surface  to  dolomite  or  quartzite,  apparently  accord- 
ing to  the  manner  in  which  displacements  have  altered  the  primary 
relations  among  the  rocks.  These  relations  are  quite  like  those 
to  be  noted  farther  south  in  Bristol  and  Middlebury,  and  those 
which  the  writer  has  described  for  the  Brandon  region. 

The  southern  portion  of  Monkton  ridge,  south  and  southeast 
of  East  Monkton  village,  is  largely  composed  of  sheared  quartzite ; 
but,  as  will  be  mentioned  again  later,  in  the  northwestern  part  of 
Bristol  the  quartzite  apparently  passes  beneath  massive,  gray, 
siliceous  dolomite  which  lies  to  the  east  of  interbedded  dolomites 
and  quartzites  in  the  northeastern  part  of  New  Haven  township. 

The  outcropping  rock  along  the  road  that  runs  through  the 
valley  of  Pond  Brook  is  quartzite ;  but  probably  this  quartzite  was 
once  overlain  by  dolomite  like  that  which  occurs  at  the  northern 
end  of  the  vallev,  to  the  east  of  Monkton  Ridge  village,  as  noted 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  241 

above,  and  presumably  the  softer  rock  has  been  largely  eroded 
over  what  is  now  the  floor  of  the  valley. 

The  western  face  of  Hogback  Mt.  is  steep  and  marked 
by  prominent  scarps. 

No  marbly  limestone  was  noted  among  the  Cambrian  rocks 
just  described  for  Monkton.  Its  absence  seems  to  be  correlated 
with  the  relatively  higher  topographic  levels  of  the  members  of 
the  Lower  Cambrian  series  in  this  township.  The  marble  ap- 
pears to  the  south  and  southwest  in  New  Haven. 

Stai'ksboro  Township. 

(Burlington  and  Middlebury  topographic  sheets.) 

Location.  Starksboro  lies  east  of  Monkton  and  the  north- 
eastern part  of  Bristol. 

General  description.  Lewis  Creek  has  its  source  in  the  hills 
of  Starksboro.  The  stream  from  the  junction  of  its  headwater 
tributaries  flows  north  across  the  township  through  a  valley  that 
separates  Hogback  Mt.  from  the  main  range.  The  floor  of 
the  valley  is  dotted  with  hills.  As  noted  above,  it  is  a  structural 
basin  secondarily  modified  by  the  erosion  of  much  of  the  rela- 
tively soft  rock.  The  hills  over  its  floor  are  formed  of  either 
quartzite  or  dolomite  whose  beds  during  the  period  of  their  com- 
pression were  folded  and  sheared  and  now  often  stand  on  end. 

Some  of  the  special  features  of  the  Starksboro  area  have  been 
described  by  N.  C.  Dale.^ 

The  western  wall  of  the  valley  is  formed  by  the  eastern  face 
of  Hogback  and  is  marked  by  numerous  scarps.  The  mountain 
is  broken  by  transverse  faults  along  which  erosion  has  worked  to 
give  a  serrated  skyline  to  the  ridge.  Less  prominent  scarps  occur 
to  the  east. 

A  feature  to  be  noted  is  the  apparent  absence  of  the  so-called 
interbedded  series,  which  is  a  condition  apparently  to  be  correlated 
with  thrust  displacements  which  elevated  older  rocks  against 
younger  ones  and  not  necessarily  with  the  original  absence  of 
these  beds  over  the  area  in  question. 

The  rocks  forming  the  hills  to  the  east  of  the  Starksboro 
road  were  not  inspected  in  Starksboro  township,  except  in  a  small 
area  around  South  Starksboro  village,  which  will  be  more  con- 
veniently described  in  connection  with  Bristol  township. 

Fanton  Township. 

(Port  Henry  topographic  sheet.) 

Location.  Panton  borders  the  lake  and  lies  between  Ferris- 
burg  on  the  north  and  Addison  on  the  south.  Its  eastern  bound- 
ary is  formed  by  a  portion  of  Otter  Creek  which  separates  it 
from  the  town  of  Waltham. 


1  Twelfth  Report  of  the  State  Geologist,  p.  43. 


242  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

General  description.  In  Panton  the  hard  rocks  are  exten- 
sively concealed  by  surface  material,  and  wholly  so  over  the 
central  portion  of  the  township  west  and  east  of  Dead  Creek.  In 
the  western  part,  outcrops  are  confined  to  the  lake  shore  and  to 
a  low  ridge  that  lies  between  it  and  the  road  running  from  north 
to  south  across  the  township,  through  Panton  village,  and  in  the 
eastern  part  to  scattered  exposures  to  the  west  of  Otter  Creek. 

The  shore  section  beginning  in  Ferrisburg,  two-thirds  of  a 
mile  north  of  the  Panton  line,  shows  black  shales  pitching  north- 
erly which  yielded  scattered  graptolites  and  brachiopods.  These 
shales  southward  pass  conformably  into  others  with  more  numer- 
ous limestone  bands  and  these  are  underlain  conformably  by 
thinly-bedded  limestones  full  of  characteristic  Trenton  species. 
The  pitch  of  these  various  beds  is  in  a  general  northerly  direction. 
Southward  is  thickly-bedded,  more  massive  limestone  which  re- 
sembles the  Black  River.  The  so-called  Black  River  beds  are 
somewhat  folded  so  as  to  give  at  some  places  a  westerly  dip  and 
an  unusually  massive  appearance  when  viewed  from  the  west. 
Southward  are  other  massive  limestone  beds  of  different  lithology 
and  strongly  brecciated.  These  rocks  gave  two  small  Maclurea- 
like  coils  on  the  weathered  surface  and  it  is  thought  that  some 
Chazy  rocks  are  at  this  place  involved  in  the  shore  section.  The 
brecciated  limestone  southward  lies  against  black  shales  which  are 
somewhat  crushed.  The  contact  is  a  short  distance  north  of 
Arnold  Bay.  From  this  contact  the  black  shales  continue  south- 
ward for  a  short  distance  with  southerly  pitch,  and  then,  with 
change  of  pitch  to  north,  to  and  around  Arnold  Bay,  where  they 
form  the  small  promontory  on  its  southern  side. 

The  structural  relation  of  the  brecciated  limestone  to  the 
shale,  north  of  Arnold  Bay,  is  far  from  clear.  There  is  no  doubt 
that  the  limestone  is  much  older  than  the  shale.  The  crushing  of 
the  latter  near  the  contact  seems  slight,  but  if  taken  with  the  other 
disturbance  shown  by  the  southward  tilting  of  the  shale  beds,  it 
is  possible  to  reconcile  the  conditions  with  the  idea  of  an  upward 
movement  of  the  older  rock  into  the  shales  which  was  probably 
preceded  by  brecciation  of  the  limestone  at  depth.  The  folding 
shown  by  the  somewhat  massive,  so-called  Black  River  beds  north 
of  the  brecciated  limestone  indicates  that  the  rocks  have  been 
under  compression  and  that,  therefore,  the  contact  in  question  is 
probably  one  of  thrust. 

East  of  Arnold  Bay  and  the  shore  road  is  a  low  ridge.  Just 
east  of  the  shore  road  and  south  of  the  one  running  from  Arnold 
Bay  to  Panton  village  are  low  ledges  of  what  appeared  to  be 
Black  River  beds  dipping  easterly.  Farther  south  along  this 
ridge  are  numerous  outcrops  of  what  appeared  to  be  Chazy  beds 
and  still  farther  south,  others  which  appear  to  be  part  of  the 
Beekmantown.  Eastward  to  the  west  of  and  sometimes  along  the 
road  running  south  from  Panton  village  the  Chazy  rocks  form  an 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  243 

almost  continuous  outcrop  for  over  two  miles  and  extend  into 
Panton  village.  In  the  village,  rocks  that  appeared  to  be  of  Black 
River  age  lie  on  the  east  side  of  the  road,  north  and  south  of  the 
one  running  to  Vergennes.  Columnaria  was  found  in  bowlders, 
but  not  in  place. 

From  the  meridian  of  Panton  village  eastward  the  surface 
is  formed  of  clay  and  outcrops  are  lacking  as  far  east  as  the  low 
ridge  about  two  miles  east  of  Dead  Creek. 

In  the  southwestern  part  of  Vergennes  at  a  road  metal 
quarry  is  dark  gray,  magnesian  limestone  which  is  conspicuously 
brecciated  at  some  places.  The  rock  is  like  that  at  the  falls  in 
the  city  and  is  probably  a  part  of  the  Beekmantown  by  compari- 
son with  rocks  in  the  Shoreham  section.  Farther  south  along  a 
road  running  west  of  this  quarry  are  outcrops  of  gray,  magnesian 
rock  and  quartzite  which  resemble  as  much  as  anything  in  the 
region  the  rocks  of  Mt.  Independence  in  Orwell,  and  seemed  to 
the  writer,  without  much  doubt,  to  represent  the  lower,  part  of 
Brainerd  and  Seely's  Beekmantown  and  their  so-called  "Pots- 
dam" as  found  in  Shoreham.  The  outcrops  of  these  rocks  are, 
however,  few  and  of  small  extent  and  the  correlation  is  tentative. 

For  the  rest,  little  may  apparently  be  learned  of  the  hard 
rock  underlying  this  township. 

If,  as  seems  likely,  the  rocks  in  the  eastern  part  of  the  town- 
ship are  Lower  Beekmantown  and  those  to  the  west  beneath  the 
clay  are  shales,  the  former  have  probably  ridden  over  the  latter 
by  thrust  much  as  they  have  north  of  Highgate  Springs  and 
also  to  the  south  in  Shoreham  and  Orwell.  The  massive  rocks  in 
the  western  part  of  the  township  probably  represent  an  independ- 
ent upthrust  into  the  younger  shales. 

Waltham  Township. 

(Port    Henry   and   Middlebury   topographic   sheets.) 

Location.  Waltham  is  separated  on  the  west  from  Panton 
and  the  northeastern  part  of  Addison,  which  lies  south  of  Panton, 
by  Otter  Creek.  On  the  north  it  is  bounded  by  Vergennes  and 
part  of  Ferrisburg  and  on  the  east  and  south  by  New  Haven. 

General  description.  Waltham  is  distinguished  topograph- 
ically by  the  considerable  elevation  known  as  Buck  Mt.  De- 
scription may  conveniently  begin  with  the  rocks  lying  between 
Otter  Creek  and  the  mountain. 

A  road  to  Weybridge  runs  directly  south  from  Vergennes  on 
the  west  side  of  Buck  Mt.  About  a  mile  south  of  Vergennes, 
between  the  road  just  mentioned  and  another  running  east  of 
the  mountain  to  New  Haven  Junction,  is  strongly  sheared,  blue 
limestone  of  probably  Trenton  age.  Fossils  have  largely  been 
destroyed.  A  half  mile  farther  south  along  the  same  meridian 
and  east  of  the  Weybridge  road  is  very  much  mashed  limestone 


244  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

having  the  Hthological  characters  of  the  Chazy  and  often  carry- 
ing numerous  small  indistinguishable  fossils  and  recognizable 
specimens  of  Girvanella.  The  rocks  have  been  sheared,  but  a 
general  easterly  dip  may  be  discerned.  Along  the  strike  of  the 
beds  the  dip  changes  from  a  high  to  a  moderate  angle.  East  of 
these  Chazy  rocks  are  outcrops  of  Trenton  limestone  beds  also 
dipping  easterly. 

Eastward  towards  the  road  running  from  Vergennes  to 
New  Haven  Junction,  beds  of  limestone  form  an  anticline  along 
meridians  which  are  occupied  farther  south  by  the  Red  Sandrock 
of  Buck  Mt.  The  limestone  is  not  like  the  Trenton  beds  just 
west  of  it,  but  in  its  general  characters  more  closely  resembles 
the  dove-gray  beds  carrying  yellow-weathering  or  chamois-colored 
layers  and  patches  which  are  intermingled  with  interbedded 
quartzites  and  dolomites  in  the  areas  farther  east.  It  lies  on  the 
meridians  of  the  Chazy  limestone  at  Marsh  Hill,  east  of  the  city 
of  Vergennes.  It  was  apparently  regarded  as  Trenton  by  Seely 
and  is  apparently  so  shown  on  his  "Geological  Map  of  Addison 
County"  (see  Seventh  Report  of  the  State  Geologist),  but  this 
map  fails  to  depict  in  any  detailed  or  accurate  manner  the  various 
rock  outcrops  in  Waltham, 

North  of  Buck  Mt.  a  cross  road  joins  the  Weybridge  and 
New  Haven  roads.  South  of  this  cross  road,  along  the  one 
to  Weybridge,  Chazy  limestone,  dipping  easterly  and  carrying  M. 
magna  and  Girvanella  forms  numerous  outcrops.  South  of  these 
Chazy  beds  on  the  west  side  of  the  road,  opposite  the  school  house, 
is  somewhat  sheared,  Trenton  limestone  with  many  surface  mark- 
ings of  fossils.  Prasopora  was  found  at  this  locality.  The  beds 
dip  easterly  and  are  filled  with  many  small  veins  of  calcite.  A 
mile  to  the  south  on  both  sides  of  the  road,  beds  of  Chazy  lime- 
stone, dipping  easterly,  form  conspicuous  ledges.  On  the  east 
side  of  the  road  the  rock  is  visibly  sheared,  but  its  fossils  are 
distinct  and  included  distorted  specimens  of  M.  magna  and  many 
specimens  of  Girvanella.  East  of  these  beds  are  much  altered 
Black  River  rocks,  full  of  small  veins  of  calcite,  but  still  showing 
the  characteristic  surface  markings  of  the  Black  River  beds  of 
the  lake  region.  The  Black  River  beds  dip  easterly.  Some  of 
the  soil-covered  spaces  which  now  separate  the  Chazy  and  Tren- 
ton outcrops  may  be  underlain  by  Black  River  rocks. 

The  various  rocks  along  the  Weybridge  road  just  described 
belong  to  the  lake  series.  They  are  the  southward  extension  of 
similar  rocks  around  the  city  of  Vergennes  and  those  which  lie 
north  of  the  city  in  Ferrisburg.  All  the  various  kinds  of  rocks 
are  visibly  sheared  at  some  places  and  show  other  effects  of  com- 
pression On  the  southwestern  side  of  Buck  Mt.,  massive  Chazy 
beds  may  be  followed  a  half  mile  east  of  the  Weybridge  road  and 
seem  to  be  repeated  across  the  strike  as  though  piled  on  each 
other  by  successive  thrusting,  but  in  the  presence  of  such  ap- 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  245 

parent  repetition  of  beds  in  this  region  it  is  not  always  easy  to 
decide  whether  the  conditions  are  due  to  thrusting  or  normal 
faulting,  even  when  there  can  be  no  doubt  that  as  a  whole  the 
rocks  involved  have  been  disturbed  b}'  thrusts. 

The  rocks  along  the  Weybridge  road  are  on  meridians  to 
the  east  of  those  occupied  by  the  brecciated,  gray,  magnesian  lime- 
stones at  Vergennes  falls  and  the  similar  rocks  south  of  the  city. 
From  the  fact  that  north  of  Vergennes  the  Chazy,  with  easterly 
dip,  extends  to  meridians  west  of  the  falls  makes  it  difficult  to 
visualize  the  relations  of  these  various  massive  rocks  to  each 
other.  It  seems  probable  that  in  a  good  many  cases,  massive 
Lower  Ordovician  strata  broke  at  depth  and  were  shoved  upward 
into  younger  rocks  in  such  way  that  the  younger  beds  on  one 
side  were  underthrust  and  on  the  other  overthrust.  The  hori- 
zontal component  varied.  The  brecciated  condition  of  the  rock 
at  Vergennes  falls  and  south  of  the  city  may  be  the  expression  of 
internal  deformation  within  the  Beekmantown  rocks  on  either  the 
underthrust  or  overthrust  border  of  the  ruptured  mass.  The 
rocks  in  eastern  Panton  which  have  been  described  and  regarded 
as  probably  representing  the  Lower  Beekmantown  may  have 
underthrust  the  rocks  along  the  Weybridge  road,  in  a  general 
sense,  and  have  overthrust  the  shales  which  are  thought  to  lie 
to  the  west  of' them. 

It  is  interesting  to  note  that  the  calcareous  rocks  in  eastern 
Panton  and  the  western  part  of  Waltham  are  on  meridians  oc- 
cupied by  the  Red  Sandrock  formation  of  Snake  Mt.  in  western 
Weybridge  and  the  southeastern  part  of  Addison. 

East  of  the  Weybridge  road  passing  west  of  Buck  Mt., 
the  calcareous  rocks  above  described  in  general  lie  at  the  base  of 
a  series  of  scarps  that  bound  the  mountain  on  the  west.  The 
drift  that  has  been  piled  against  these  scarps  conceals  contacts 
between  the  limestone  and  the  Sandrock.  The  scarps  mark  planes 
of  faulting;  but  it  is  not  clear  whether  the  present  structural 
relations  of  the  rocks  involved  are  due  to  reverse  faulting  and 
modifications  simply  from  erosion,  or  whether  primary  thrusts 
have  been  modified  by  tension  faulting  as  well  as  by  erosion. 

East  of  the  scarps  the  surface  of  the  mountain  slopes  grad- 
ually eastward  across  the  eroded  edges  of  red  quartzite  beds 
which  dip  gently  to  the  east.  East  of  the  mountain,  in  the 
western  part  of  New  Haven  township,  the  surface  is  generally 
covered  with  drift,  but  there  are  some  exposures  of  red  quartzites 
along  the  direct  road  from  New  Haven  Junction  to  Vergennes. 

In  the  southeastern  corner  of  Waltham  are  interbedded  mem- 
bers of  the  Lower  Cambrian  series  which  are  probably  to  be 
thought  of  as  stratigraphically  above  the  red  quartzite  forming 
the  eastern  slope  of  Buck  Mt.  For  the  most  part  these  mem- 
bers of  the  interbedded  series,  which  carries  some  red  quartzite, 
dip  to  the  east,  but  on  their  western  margin  a  slight  westerly  dip 


246  RETORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

was  noted  indicatinj^  a  small  amount  of  flexure  in  these  rocks. 
These  interbedded  dolomites  and  quartzites  join  southward  with 
others  in  New  Haven  township  which  will  be  described  beyond, 
and  the  red  quartzite  of  Buck  Mt.  also  extends  southward  with 
reduced  elevation  into  New  Haven  at  the  south. 

New  Haven  Township. 

(Middlebury  topographic  sheet.) 

Location.  This  township  is  one  of  irregular  boundaries. 
In  general  it  is  bounded  by  Waltham  on  the  west,  by  Ferrisburg 
and  Monkton  on  the  north,  by  Bristol  on  the  east  and  by  Middle- 
bury  and  Weybridge  on  the  south. 

General  description.  In  a  small  jog  in  the  very  northwest- 
ern part  of  the  town  are  outcrops  of  Chazy  limestone  which  are 
the  southward  continuation  of  the  Chazy  beds  along  the  Wey- 
bridge road  in  the  southern  part  of  Waltham.  The  rocks  carry 
Middle  Chazy  fossils  and  dip  to  the  east. 

A  mile  to  the  south  of  these  rocks  is  an  assemblage  of  dove- 
colored  limestones,  with  buff-gray  layers  which  now  frequently 
appear  as  patches  among  their  associated  dove-colored  beds. 
These  rocks  are  not  like  the  Chazy  beds  just  north  of  them ;  but 
are  somewhat  like  the  calcareous  rocks  lying  north  of  Buck 
Mt.  and  very  much  like  other  rocks  found  on  meridians  farther 
east,  more  or  less  intermingled  at  the  present  surface  with  Lower 
Cambrian  rocks  and  which  are  very  abundant  over  large  areas  in 
the  townships  of  Weybridge  and  Middlebury.  In  northwestern 
New  Haven  these  beds  are  usually  much  disturbed,  but  at  some 
places  may  be  seen  to  have  easterly  dip.  In  their  various  litho- 
logical  features  these  rocks  are  not  easily  correlated  with  any  of 
the  members  of  lake  series  proper;  fossils  are  absent  or  obscure 
and  their  age  has  been  much  of  a  puzzle  to  all  students  of  the 
region. 

A  few  rods  north  of  the  junction  of  the  road  from  Addison 
village  to  New  Haven  Junction,  and  the  one  from  Vergennes  to 
Weybridge  passing  west  of  Buck  Mt.,  members  of  this  forma- 
tion of  dove  and  gray  rocks  rest  on  crushed  and  .sheared,  bluish- 
black,  shaly  limestone  that  has  strong  resemblance  to  the  Trenton. 
The  contact  may  be  plainly  seen  on  the  eastern  side  of  the  Ver- 
gennes road.  It  seems  to  be  a  thrust  contact.  About  a  half  mile 
to  the  west  on  the  north  side  of  the  Addison  road  are  graptolite 
shales  with  members  of  the  dove  and  gray  series  forming  the 
surface  above  the  shales  which  are  exposed  in  a  cut  in  the  bank 
of  the  road.  East  of  the  dove  and  gray  beds  is  red  quartzite 
which  extends  south  from  Buck  Mt.  Farther  to  the  east  and 
southward  the  hard  rock  passes  under  clay  or  drift. 

About  a  mile  and  a  half  east  of  Otter  Creek  and  the  out- 
crops just  described  is  a  low  ridge   formed  by  the  interbedded 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  247 

rocks  of  the  Cambrian,  which  are  the  direct  southward  extension 
of  the  similar  rocks  in  the  southeastern  part  of  Waltham  and 
which  still  hold  to  a  gentle  easterly  dip.  Traced  southward  these 
interbedded  rocks  pass  under  drift  for  a  short  distance.  Then 
along  the  same  meridian  are  scattered  outcrops  of  gray,  siliceous 
dolomite  which  continue  to  within  a  mile  and  a  half  of  Wey- 
bridge  village. 

Northeast  and  east  of  Weybridge  village,  to  the  west  of  and 
along  the  railroad  track,  are  numerous  exposures  of  the  dove- 
colored  rock  and  its  bufif-gray  associate.  In  their  outcrops  about 
a  mile  southwest  of  Spring  Grove  Camp  Ground,  these  rocks  fre- 
quently stand  on  end  and  show  evidence  of  extreme  compression. 
Similar  rocks  occur  southwest  of  New  Haven  Junction,  where 
they  show  the  same  evidence  of  compression  and  are  strongly 
sheared. 

East  of  the  Rutland  R.  R.  track  at  numerous  places,  over  a 
strip  about  a  mile  and  a  half  wide  extending  from  the  northern 
to  the  southern  boundary  of  the  township,  are  exposures  of  more 
or  less  striped  or  marbly  limestone.  Two  miles  north- northeast 
of  New  Haven  Junction,  near  the  Ferrisburg  line,  outcrops  of 
gray,  siliceous  dolomite  or  interbedded  dolomite  and  quartzite  at 
places  roughly  alternate  across  the  strike  with  outcrops  of  striped 
blue  or  marbly  limestone.  The  structural  relations  are  very 
obscure,  but  at  places  there  seems  to  be  suggestion  that  the  marble 
lies  on  the  dolomite  and  at  others  that  the  interbedded  rocks  have 
been  thrust  over  the  marble. 

The  surface  of  the  hill  just  east  of  the  quarry  of  the  "Green 
Mountain  Lime  Works,"  gives  massive,  striped  bluish  and  gray 
rocks  interbedded  with  some  siliceous  layers  and  others  that 
weather  to  a  grayish-buff.  The  gray  rock  carries  obscure  coils, 
but  a  careful  scrutiny  of  weathered  surfaces  did  not  give  anything 
definite.  In  the  quarry  of  the  lime  works  the  rock  is  generally 
more  or  less  massive  and  crystalline  and  is  practically  a  marble. 
Planes  of  stratification  are  visible,  but  the  beds  are  much  de- 
formed and  dip  and  twist  in  various  directions.  In  the  fields 
near  the  quarry,  in  what  appear  to  be  surface  exposures  of  rocks 
like  those  in  the  quarry,  are  rocks  quite  similar  to  those  just  de- 
scribed for  the  hill  east  of  the  quarry. 

Northward  across  the  road  from  the  quarry,  white,  marbly 
limestone  is  intermingled  with  gray  dolomite.  Still  farther  north, 
along  the  so-called  "Plank  road"  in  the  southwestern  corner  of 
Ferrisburg,  white,  marbly  limestone  lies  south  of  the  road,  just 
west  of  a  mass  of  gray,  siliceous  dolomite  showing  bedding  well 
marked,  and  on  the  north  side  of  the  road,  on  the  same  meridian 
with  the  marble,  is  a  low  ridge  composed  of  interbedded  quartzite 
and  dolomite,  at  this  place  largely  quartzite,  showing  a  gentle 
anticlinal  buckle  pitching  gently  to  the  north.  A  fourth  of  a  mile 
to  the  west  is  gray  dolomite  dipping  at  a  low  angle  to  the  east ; 


248  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

and  about  the  same  distance  to  the  east  is  gray  dolomite  again, 
which  northward  along  the  same  meridian  gives  place  to  inter- 
bedded  rocks  lying  nearly  flat. 

The  field  relations  in  the  absence  of  definite  contacts  do  not 
permit  positive  statement  of  structure ;  but  at  the  time  of  inspec- 
tion it  appeared  that  the  primary  relation  was  that  of  marble 
resting  on  Cambrian  rocks  and  that  the  latter  had  been  thrust 
against  and  sometimes  over  the  former.  It  will  appear  from 
later  discussions  that  the  primary  relation  of  the  marble  probably 
was  that  just  indicated  and  that  in  several  cases  the  rocks,  whether 
massive  dolomite  or  interbedded  dolomite  and  quartzite  on  which 
the  marble  lay,  were  broken  and  thrust  over  the  marble. 

Eastward  towards  Bristol,  along  the  "Plank  road,"  in  the  ex- 
treme southwestern  corner  of  Monkton,  but  practically  on  the 
New  Haven  line,  are  ledges  of  massive  dolomite  forming  the  low, 
southern  portion  of  Monkton  ridge.  Southward  these  rocks  dis- 
appear beneath  Cedar  Swamp ;  but  south  of  the  swamp,  on  the 
same  meridian,  and  just  south  of  the  Bristol  R.  R.  track,  begins  a 
ridge  of  the  interbedded  series.  Near  the  crossing  of  the  New 
Haven-Bristol  road  and  the  railroad  track  are  beds  of  red  quartz- 
ite which  dip  gently  to  the  west.  Slightly  to  the  southeast  is  a 
distinct  scarp  on  the  western  side  of  a  considerable  hill  of  inter- 
bedded dolomites  and  quartzites.  Two-thirds  of  a  mile  east, 
across  a  low  area,  is  another  hill  or  ridge  of  the  interbedded  rocks, 
which  on  the  western  side  are  terribly  jammed  and  puddled. 
Eastward  the  beds  undulate  and  stand  at  various  angles  of  dip, 
but  at  the  summit  of  the  eastern  slope  they  may  be  seen  to  dip 
gently  to  the  west.  The  eastern  slope  of  the  hill  from  these  beds 
down  to  the  road  that  runs  from  New  Haven  Mills  northward 
towards  Monkton  is  drift  covered ;  but  southward,  northeast  of 
New  Haven  Mills,  is  whitish,  granular  quartzite  apparently 
overlain  by  gray  dolomite.  The  quartzite  outcrops  on  both  sides 
of  the  dolomite  and  dips  to  the  east;  the  dolomite  is  sheared  so 
that  its  bedding  is  obscured ;  but  at  places  it  seems  to  be  standing 
on  end. 

South-southwest  of  New  Haven  Mills,  south  of  the  river,  on 
the  meridian  of  the  quartzites  and  dolomites  north-northwest  of 
the  village,  is  another  ridge  of  the  interbedded  rocks.  On  the 
west  of  this  ridge  the  rocks  dip  westerly,  but  on  the  eastern  slope 
they  form  the  distorted,  pushed-up  eastern  limb  of  an  anticlinal 
fold.  The  effects  of  compression  at  this  place  beggar  descrip- 
tion. The  often  somewhat  massive  quartzite  beds  are  jammed 
into  Z-shaped  folds  and  strongly  sheared  withal  and  wave  back 
and  forth  along  the  strike.  The  structure  is  identical  with  that 
shown  by  similar  rocks  east  of  Brandon,  as  elsewhere  described, 
except  that  the  jamming  is  more  severe.  The  interbedded  rocks 
may  be  followed  along  this  ridge  southward  to  the  Middlebury 
line  and  have  anticlinal  structure  throughout.     Near  the  southern 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  249 

boundary  of  the  township  these  rocks  are  only  a  mile  from  the 
quartzite  scarp  along  the  edge  of  the  plateau,  from  which  they 
are  separated  by  the  ledges  of  massive,  gray  dolomite  forming 
the  hill  known  as  the  "Cobble." 

North  of  New  Haven  Mills,  partly  in  Bristol,  are  several 
low,  detached  hills  of  gray  dolomite,  some  of  which  show  scarps 
on  the  west.  Sheared,  gray,  siliceous  dolomite  forms  the  bed  and 
banks  of  the  river  at  New  Haven  Mills. 

The  interbedded  rocks  forming  the  hill  with  the  prominent 
scarp  southeast  of  New  Haven  village  join  at  the  surface  with 
similar  rocks  along  the  road  that  runs  directly  south  from  the 
village  along  which  they  outcrop  through  a  distance  of  two  miles. 
One-half  mile  west  of  the  road  and  about  a  mile  south-southwest 
of  New  Haven  village  are  outcrops  of  bluish-white  marble, 
flanked  on  the  west  by  striped  bluish  limestone  with  spots  of 
Tnarbly  rock,  all  dipping  easterly  and  all  marked  by  strong  flow- 
shearing.  The  striped  rock  has  much  superficial  resemblance 
to  some  Middle  Chazy  of  the  lake  series.  No  fossils  have  sur- 
vived the  severe  deformation  of  the  rock.  About  a  half  mile 
west  of  these  outcrops  are  others  of  similar  rock  on  the  east  side 
of  the  road  from  Spring  Grove  Camp  Ground  to  New  Haven 
village,  and  south  of  the  latter  are  still  other  outcrops  of  bluish 
limestone  somewhat  involved  with  bui¥-weathering  layers. 

Two  miles  southeast  of  Spring  Grove  Camp  Ground,  in  the 
angle  of  the  roads,  are  outcrops  of  bluish  and  marbly  Hmestone 
intermingled  with  fragmentary  patches  of  the  interbedded  series. 
Since  these  rocks  lie  on  the  meridians  of  the  interbedded  rocks 
farther  north  it  seemed  likely  that  the  marble  had  actually  been 
overridden  by  the  Lower  Cambrian  rocks.  The  relations  again 
are  similar  to  those  among  the  interbedded  rocks  and  the  marble 
around  Brandon. 

On  the  meridian  of  the  rocks  described  in  the  last  paragraph, 
south  of  New  Haven  River  and  west  of  Muddy  Brook,  is  a  ridge 
which  extends  southward  into  Middlebury  township.  Great  con- 
fusion prevails  among  the  surface  rocks  along  this  ridge.  At  its 
northern  end,  which  is  the  portion  included  in  New  Haven,  on  the 
east  slope,  gray  dolomite  is  intermingled  with  striped  blue  lime- 
stone. Westward  over  the  summit  the  striped  blue  limestone  is 
intermingled  with  patches  of  interbedded  dolomites  and  quartzites, 
the  latter  often  forming  exposures  of  considerable  size,  with  well- 
defined  bedding  and  dip.  In  some  places  the  members  of  the  in- 
terbedded series  lie  flat,  in  others  they  dip  to  the  west  and  in  others 
the  structure  may  not  be  made  out.  A  survey  of  the  hill  showed 
that  quartzites  and  dolomites  are  often  involved  with  the  lime- 
stone in  such  a  way  as  to  give  the  appearance  of  being  inter- 
stratified.  The  surface  is  greatly  broken  by  gullies  and  knolls 
of  various  dimensions.     In   some  places  the   striped  blue   rock 


250  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

shows  in  massive  ledges ;  in  others  the  rock  is  apparently  all  gray, 
siliceous  dolomite. 

The  secondary  structural  features  are  very  complicated ;  but 
the  general  field  relations  seemed  to  point  to  involved  thrust  rela- 
tions like  those  which  have  been  described  for  the  region  around 
Brandon.  Similar  conditions  will  be  described  for  Middlebury 
in  subsequent  pages. 

No  fossils  were  found  although  it  seemed  as  though  they 
should  be  and  diligent  search  was  made. 

East  of  this  ridge,  near  Muddy  Brook  and  on  the  township 
line,  is  a  marble  quarry,  known  as  "marble  ledge."  Marble  also 
outcrops  to  the  north  of.  the  quarry,  just  south  of  New  Haven 
River.  Gray  dolomite  forms  the  eastern  wall  of  the  quarry  and 
marks  the  surface  along  which  the  marble  has  been  quarried. 
Again,  the  conditions  are  precisely  like  those  in  some  of  the  quar- 
ries around  Brandon. 

Wing  was  reported  by  Dana^  to  have  found  an  Orthoceras, 
resembling  O.  primigeniunt  Hall  (a  Calciferous  form),  in  rocks, 
a  little  way  south  of  the  quarry,  east  of  the  brook,  in  Middlebury. 
On  the  basis  of  this  fossil  the  rocks  were  assigned  to  the  Beek- 
mantown  by  Dana  and  later  by  Seely.  In  fact  all  the  various 
rocks  that  have  just  been  described  for  the  southwestern  part  of 
New  Haven  were  called  Beekmantown  by  Seely.  A  great  deal 
of  the  marbly  and  striped  limestone  in  the  writer's  opinion  has 
more  lithological  resemblance  to  the  Chazy  and  it  is  certain  that 
Lower  Cambrian  dolomites  and  interbedded  rocks  are  involved 
with  the  marbly  limestone.  The  writer  tried  to  find  the  spot  which 
Wing,  Dana  and  Seely  visited,  following  carefully  the  directions 
given  by  Dana  (loc.  cit.)  but  failed  to  note  the  outcrop. 

Dana  further  mentions  discovery  by  Wing  of  other  fossils- 
a  half  mile  northwest  of  the  Orthoceras  locality,  and  apparently 
on  the  eastern  slope  of  the  ridge  west  of  Muddy  Brook.  At  thi^ 
locality  "and  apparently  in  the  same  formation  with  the  last,  there 
are  specimens  resembling  Ophileta  compacta;  there  was  also  found 
here  a  large  Maclurea." 

"About  a  mile  southwest  of  the  Middlebury  quarry  and  thirty 
or  forty  rods  west  of  Mr.  E.  Kirby's  residence,  in  an  old  orchard, 
several  distinct  convoluted  shells  were  seen  on  a  dark,  siliceous 
Hmestone  dipping  west.     The  beds  are  probably  Calciferous." 

North  and  south  of  Beldens,  in  the  fields  east  of  Otter  Creek 
and  in  the  bed  of  the  river  itself,  are  extensive  exposures  of 
usually  distinctly  bedded  gray  and  buff-weathering  rocks  which 
are  different  from  the  striped  blue  and  marbly  limestones  that  lie 
east  of  them.  These  rocks  have  also  been  called  Beekmantown. 
They  extend  southward  into  Middlebury,  where  they  present  in- 
teresting field  relations  yet  to  be  described.  The  age  of  the  rocks 
is  doubtful ;  they  may  be  part  of  the  Beekmantown,  but  in  the 

3  A.  J.  S.,  vol.  XIII,  1877,  p.  406. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  251 

writer's  opinion,  Beekmantown  has  been  employed  in  much  too 
inclusive  a  way  for  the  more  or  less  altered  rocks  over  the  east- 
ern portion  of  the  Champlain  lowland. 

Bristol  Township,  including  parts  of  Lincoln  Township. 

(Middlebury  topographic  sheet.) 

Location.  Bristol  borders  New  Haven  on  the  east.  Lincoln 
lies  east  and  southeast  of  Bristol. 

General  description.  The  southern  portion  of  Monkton  ridge 
extends  into  the  northwestern  portion  of  Bristol.  Most  of  the 
portion  of  the  ridge  included  in  Bristol  is  made  of  quartzite,  but 
massive,  gray  dolomite  occurs  at  the  southern  end  near  the  New 
Haven  line.  South  of  this  dolomite  is  Cedar  Swamp,  from  which 
at  the  south  emerge  the  interbedded  quartzites  and  dolomites  of 
the  eastern  part  of  New  Haven. 

A  surface  section  southward  from  Monkton  ridge  into  New 
Haven  thus  gives  with  interruptions  a  succession  from  quartzite 
through  gray,  massive  dolomite  to  interbedded  quartzites  and 
dolomites  and  suggests  that  this  is  the  usual  stratigraphic  sequence. 

The  valley  occupied  by  Pond  Brook  in  Monkton  extends 
southward  into  Bristol,  but  its  basin  character  gradually  fades 
southward  towards  Bristol  village  owing  to  the  falling  oft*  in 
elevation  of  the  southern  portion  of  Monkton  ridge. 

Bowlder  drift  topped  by  sand  plains  largely  conceals  the  hard 
rock  around  Bristol  village  west  of  Hogback  Mt.  Gray,  siliceous 
dolomite,  dipping  westerly,  outcrops  northwest  of  the  village  and 
southwest  of  it,  west  of  "Bristol  Flats,"  other  dolomite  marks 
the  northward  extension  of  the  rocks  at  and  north  of  New  Haven 
Mills. 

South  of  Bristol  village,  to  the  east  of  Bristol  Flats  and 
just  east  of  the  road  that  runs  along  the  eastern  edge  of  the  Flats, 
the  rock  is  largely  a  gray  or  brownish-gray,  granular  quartzite, 
dipping  easterly;  but  eastward  at  places  near  the  foot  of  South 
Mt.  the  quartzite  dips  westerly.  Southward,  gray  dolomite  form- 
ing the  northern  end  of  "Cobble"  hill,  conceals  the  quartzite. 

In  the  township  of  Bristol,  west  of  Hogback  and  South  Mt., 
the  underlying  rock  is  thus  seen  to  be  quartzite  with  overlying 
dolomite  which  form  a  shallow,  synclinal  fold,  suggesting  that 
the  valley  of  Pond  Brook  is  primarily  a  syncline  which  has  been 
modified  by  faulting. 

In  Bristol,  as  in  Monkton,  the  western  face  of  Hogback  shows 
a  succession  of  scarps  along  the  strike.  The  rock  along  these 
scarps,  which  were  inspected  at  many  places,  is  essentially  a 
quartzite  which  is  usually  strongly  sheared  and  much  like  some 
of  the  rock  that  has  been  described  for  the  hilly  land  east  of  St. 
Albans  and  Milton.     In  spite  of  shearing  the  bedding  is  visible 


252  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

and  dips  to  the  east.  The  easterly  dip  is  well  shown  on  the 
mountain  at  the  ledge  known  locally  as  "Table  Rock." 

New  Haven  River  enters  the  lowland  through  a  gap  between 
Hogback  and  South  Mt.  Along  this  pass  the  quartzite  may  be 
observed  at  many  places  dipping  easterly  and  the  southern  end 
of  Hogback  may  clearly  be  seen  to  be  bounded  by  a  series  of 
scarps  marking  fault  displacements  across  the  strike.  The  river 
has  availed  itself  of  these  lines  of  weakness. 

At  Ackworth,  ledges  of  quartzite  are  abundant.  The  dip  is 
easterly  at  a  small  angle  and  the  rocks  exhibit  little  or  no  internal 
deformation.  There  is  a  slight  northerly  pitch.  On  the  road 
towards  West  Lincoln,  about  one-third  of  a  mile  east  of  Ack- 
worth, the  dip  is  westerly. 

The  valley  of  Beaver  Brook  and  Baldwin  Creek  north  of 
Ackworth  is  the  southward  continuation  of  the  valley  of  Lewis 
Creek  in  Starksboro.  It  is  primarily  of  synclinal  structure,  but 
is  modified  by  faulting.  The  eastern  face  of  Hogback  shows 
scarps  marking  faults.  A  mile  and  a  half  north  of  Ackworth, 
gray  dolomite  on  the  west  side  of  the  road  dips  westerly. 

Quartzite  continues  north  from  Ackworth  east  of  the  Starks- 
boro road.  At  the  western  end  of  the  gorge  of  Baldwin  Creek  is 
strongly  sheared  rock,  much  like  that  on  the  western  side  of  Hog- 
back. In  the  bed  and  banks  of  the  stream  a  fourth  of  a  mile 
east  is  blackish  phyllite  which  is  probably  a  sheared  muddy  mem- 
ber of  the  quartzite  formation.  Two-thirds  of  a  mile  farther 
east,  in  the  north  bank  of  the  gorge,  are  impure  quartzitic  and 
calcareo-siliceous  beds  greatly  sheared  and  crushed,  which  have 
some  resemblance  to  the  interbedded  series  found  in  the  lowland 
to  the  west  of  the  plateau.  At  South  Starksboro  the  prevailing 
rocks  are  impure,  coarse  schists  which  were  interpreted  as  prob- 
ably originally  forming  impure  basal  portions  of  the  overlapping 
Lower  Cambrian  series. 

A  mile  southeast  of  South  Starksboro,  on  the  side  of  the 
road  near  a  school  house,  was  seen  a  small  exposure  of  inter- 
bedded quartzite  and  calcareous  rock.  East  of  these  beds  in  the 
fields  are  others  of  quartzite  lying  nearly  fiat. 

The  interbedded,  impure  quartzites  and  calcareous  rocks  west 
and  southeast  of  South  Starksboro  seem  to  resemble  the  inter- 
bedded series  of  the  lowland  west  of  the  plateau  closely  enough 
to  be  regarded  not  as  precise  equivalents  perhaps,  but  as  related 
members  of  a  common  formation.  It  would  seem  that  in  the 
probess  ofi  overlap  such  rocks  were  carried  eastward  into  what 
is  now  the  plateau,  just  as  gray  dolomite  was  also  carried  at  some 
places. 

The  quartzite  exposed  in  the  bed  of  New  Haven  River,  south- 
east of  Ackworth.  gives  place  southeast  of  West  Lincoln  to 
gneissic  rocks  that  are  different  from  the  sheared  rocks  that 
seem  more  or  less   definitely  to  belong  to   a   formation   which 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  253 

originally  consisted  of  various  kinds  of  sediments  and  which  is 
probably  of  Lower  Cambrian  age.  Similar  gneisses  were  noted 
near  the  river  at  Lincoln  Center  and  in  South  Lincoln  and  are 
regarded  as  probably  pre-Cambrian  and  as  forming  a  part  of 
the  floor  of  deposition  of  the  quartzite-schist-dolomite  formation. 

Three  and  a  half  miles  south  of  Bristol  village  the  "little 
notch  road"  leaves  the  lowland  and  climbs  over  the  mountain  to 
South  Lincoln.  The  western  portion  of  the  road  cuts  through 
the  southward  extension  of  the  quartzite  of  the  western  part  of 
South  Mt.  From  places  along  the  road,  east  of  the  front  range 
of  hills,  they  may  be  seen  to  be  bounded  on  the  east  by  scarps,  to 
the  east  of  which  the  surface  is  lower.  The  suggestion  which  the 
topography  gives  of  down-faulting  on  the  east  of  the  front  range 
is  supported  by  the  occurrence  of  considerable  exposures  of  gray 
dolomite  along  the  road  towards  South  Lincoln.  The  dolomite 
is  intermingled  over  large  areas  with  micaceous,  quartzitic  schist, 
which  apparently  weathers  fairly  easily,  but  it  did  not  appear 
from  any  outcrops  which  were  noted  that  the  schist  is  interbedded 
with  the  dolomite.  The  gray  dolomite  is  lithologically  much  like 
that  west  of  the  plateau.  In  some  of  its  outcrops  it  occurs  in 
undulating  folds  sheared  across  the  bedding.  This  dolomite  was 
interpreted  as  the  extension  eastward  into  the  plateau  of  the 
dolomite  that  is  found  in  what  is  now  the  lowland  to  the  west  of 
it,  and  as  part  of  the  Lower  Cambrian  series. 

Around  South  Lincoln  in  the  beds  of  streams,  foliated, 
gneissic  rocks  not  easily  interpreted  as  sheared  members  of  the 
Cambrian  formation  were  noted  and  at  the  time  of  their  inspec- 
tion seemed  to  be  probably  a  portion  of  the  pre-Cambrian  forma- 
tion of  basal  gneisses.  No  attempt  was  made  to  trace  the  quartz- 
ite-dolomite-schist  formation  into  the  eastern  part  of  Lincoln. 

While  some  of  the  members  of  the  formation,  which  is  re- 
garded as  Lower  Cambrian,  in  their  occurrence  in  the  mountains 
are  not  very  much  deformed  internally,  others  of  them  are  and 
in  some  places  shearing  or  crushing  is  severe,  and  gneissoid  or 
schistose  structure  is  common.  The  most  severely  sheared  types 
might  be  confused  with  other  rocks  and  assigned  a  different  age 
and  possibly  to  an  older  series,  without  careful  discrimination; 
but  it  seemed  that  any  of  the  gneisses  which  could  be  interpreted 
as  probably  older  than  Cambrian  are  sufficiently  different  from 
sheared  and  altered  younger  rocks  to  be  fairly  easily  distin- 
guished, at  least  within  the  areas  examined  by  the  writer.  Such 
might  not  be  the  case  farther  east  in  the  mountains. 


254  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Addison  Township. 

(Port  Henry  topographic  sheet.) 

Location.  Addison  township  borders  the  lake  and  lies  south 
of  Panton.  It  is  bounded  on  the  east  by  parts  of  Waltham  and 
Weybridge  and  on  the  south  by  Bridport. 

General  description.  Like  Panton,  a  large  part  of  the  west- 
ern portion  and  most  of  the  central  portions  are  covered  with 
clay.  Outcrops  are,  therefore,  practically  confined  to  the  lake 
shore  and  the  somewhat  hilly  eastern  part. 

From  the  Bridport  line  northward  along  shore  as  far  as 
Chimney  Point  is  clay.  At  Chimney  Point  are  beautifully  glaci- 
ated ledges  of  Chazy  with  the  beds  dipping  at  a  low  angle  to  the 
west.  Similar  beds  with  about  the  same  dip  occur  to  the  north- 
east, on  the  north  bank  of  Hospital  Creek. 

North  of  Hospital  Creek,  to  the  west  of  the  Chazy  outcrops, 
on  the  lake  shore,  are  thinly-bedded  limestones,  weathering  gray 
but  bluish  on  fresh  surfaces,  clearly  derived  from  limy  muds, 
and  full  of  characteristic  basal  Trenton  fossils.  The  beds  also 
dip  westerly  and  at  an  angle  about  like  that  of  the  neighboring 
Chazy  rocks  at  the  east.  They  have  apparently  a  slight  northerly 
pitch. 

These  Trenton  rocks  are  succeeded  along  shore  northward 
by  more  or  less  regularly  interbedded,  blackish  limestone  and 
shale.  The  limestone  members  contain  Trenton  fossils,  including 
Prasopora,  and  the  series  plainly  marks  a  transition  from  the 
"basal"  Trenton  beds  into  rocks  that  are  more  notably  shaly  and 
which  continue  along  shore  to  Potash  Bay.  The  dip  throughout 
is  gently  to  the  west.  Graptolites  were  found  at  numerous  places 
in  the  shales,  but  Triarthrus  hecki,  so  common  in  the  shales  in 
the  northern  part  of  the  lake  region,  was  not  seen.  The  shore 
section  from  Crane  Point  to  Potash  Bay  is  about  three  miles  long. 
The  dip  is  so  gentle  that  the  rocks  lie  almost  fiat.  They  seem  to 
be  broken  hardly  any,  if  at  all,  by  displacements  and  as  a  whole 
give  a  considerable  thickness  of  apparently  conformable  beds 
ranging  from  the  base  of  the  Trenton  well  up  into  the  shale 
formation. 

East  of  the  shore  section  the  hard  rocks  are  usually  beneath 
clay ;  some  apparently  Trenton  rocks  outcrop  along  the  road  north 
of  Hospital  Creek. 

In  general  the  rocks  along  shore  in  Addison  appear  to  form 
the  western  limb  of  a  gentle  anticlinal  fold.  The  apparent  struc- 
ture permits  the  interpretation  that  the  basin  of  the  lake  west  of 
Addison  was  excavated  in  shales  that  conformably  overlay  the 
rocks  that  lie  along  shore  and  that  similar  shales  extend  eastward 
beneath  the  clay.  In  other  words,  along  the  Addison  shore  there 
is  little  or  no  suggestion  of  overthrust  of  older  rocks  on  the  shales 
such  as  is  seen  in  many  other  places  along  or  near  the  lake.     If 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  255 

the  rocks  around  Chimney  and  Crane  Points  constitute  a  con- 
formable series,  Black  River  beds  should  intervene  between  the 
Chazy  and  Trenton,  by  analogy  with  conditions  at  other  places  in 
western  Vermont.  There  are  some  outcrops  on  the  road  north 
of  Hospital  Creek  which  indeed  suggest  the  Black  River,  but  if 
these  rocks  are  generally  present  they  are  for  the  most  part  con- 
cealed. 

The  eastern  boundary  of  Addison  zigzags  through  the  mass 
of  Snake  Mt.  which  lies  partly  in  this  township  and  partly  in 
Weyb ridge.  North  of  Snake  Mt.  the  eastern  boundary  follows 
Otter  Creek  to  the  Panton  line. 

The  higher  portions  of  the  mountain  are  in  Addison.  The 
rock  is  chiefly  red  quartzite,  like  that  of  Buck  Mt.  The  surface 
of  the  mountain  falls  off  abruptly  northward  and  gives  place  to 
a  clay-covered  lowland.  The  western  face  of  the  mountain  is 
marked  by  scarps,  against  which  at  places  rest  banks  of  glacial 
drift. 

Along  and  near  the  road  that  runs  just  west  of  the  moun- 
tain are  outcrops  of  limestone  which  may  now  be  described. 

From  Addison  village  a  road  runs  eastward  to  Weybridge, 
passing  north  of  Snake  Mt.  About  a  mile  east  of  the  village 
another  road  runs  southward  just  west  of  the  mountain.  East 
of  this  road  on  the  northwestern  slope  of  the  mountain  are  beds 
of  shaly  limestone  lying  nearly  flat  but  which  have  perceptible 
easterly  dip  and  are  rather  conspicuously  sheared.  These  out- 
crops yielded  a  few  Trenton  fossils.  Perhaps  150  rods  farther 
south,  along  the  roadside,  are  ledges  of  Chazy  limestone  also 
dipping  easterly  and  carrying  characteristic  fossils.  The  Chazy 
continues  southward  for  a  fourth  of  a  mile  and  is  flanked  on 
the  east  by  Black  River  beds.  A  mile  to  the  south  on  the  same 
meridian  with  these  rocks  are  shaly  limestones  which  outcrop  in- 
termittently along  the  road  to  the  Bridport  line. 

To  the  west  of  the  road  just  followed  is  another  parallel 
with  it  which  runs  through  Addison  village.  Sheared  limestone 
carrying  Trenton  fossils  and  dipping  easterly  outcrops  one-half 
mile  north  of  the  Bridport  line  and  a  mile  farther  north  are 
ledges  of  Chazy  with  easterly  dip. 

The  calcareous  rocks  lying  west  of  Snake  Mt.  apparently 
form  a  monoclinal  series  dipping  easterly,  with  the  Chazy  at 
the  base  overlain  by  Black  River  and  sheared  Trenton  limestone. 
While  the  outcrops  are  scattered,  the  field  relations  among  them 
permit  the  interpretation  just  given  and  also  the  inference  that 
the  beds  are  mainly  conformable,  although  possibly  displaced 
somewhat  with  reference  to  each  other.  About  six  miles  to  the 
west  the  same  series  dips  in  the  opposite  direction.  It  is  not 
easy  to  imagine  that  the  rocks  along  the  lake  shore  and  those 
west  of  Snake  Mt.  form  the  limbs  of  a  common  anticlinal  arch, 
for  the  dip  is  so  low  that  in  the  wide  interval  between  them  there 


256  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

seemingly  should  occur  other  outcrops  of  the  heavier  members, 
which  does  not  seem  to  be  the  case.  If  there  were  several  folds 
over  the  interval  that  now  separates  these  rocks  there  should  be 
intermediate  ridges  which  do  not  occur. 

Although  along  meridians,  now  occupied  at  the  surface  in 
Addison  by  clay,  Chazy  rocks  are  exposed  in  Panton,  this  cir- 
cumstance does  not  seem  to  justify  the-  inference  that  the  clay  in 
Addison  is  directly  underlain  by  Chazy  limestone;  for  in  Shore- 
ham  to  the  south  these  meridians  show  the  shales  as  the  surface 
rock.  As  will  be  shown  beyond,  it  is  probable  that  the  clay 
over  central  Addison  and  Bridport  is  underlain  by  shales,  and  that 
the  older  limestones  are  deeper  down.  The  key  to  the  structural 
relations  among  the  various  rocks  in  Addison  seems  likely  to  be 
found  in  the  major  kind  of  deformation  which  the  region  has 
suffered.  Snake  Mt.  is  primarily  an  unlift  of  the  older  rocks 
which  have  also  been  thrust  to  the  west.  The  limestones  west 
of  the  mountain  have  probably  suffered  similar  deformation. 
The  quartzite  of  Snake  Mt.  in  Addison  and  the  calcareous  rocks 
west  of  it  are  on  meridians  occupied  by  probable  Beekmantown 
farther  north  in  Panton. 

Weybridge  Township. 

(Port  Henry  and  Middlebury  topographic  sheets.) 

Location.  Weybridge  is  bordered  on  the  west  by  parts  of 
Addison  and  Bridport,  on  the  north  by  parts  of  Addison  and  New 
Haven,  on  the  east  by  parts  of  New  Haven  and  Middlebury,  and 
on  the  south  by  Cornwall. 

General  description.  The  eastern  slope  of  Snake  Mt.  de- 
scends into  the  western  part  of  Weybridge.  All  the  outcrops  in- 
spected west  of  the  Lemon  Fair  are  of  Red  Sandrock,  which  dips 
to  the  east. 

Clay  forms  the  surface  over  much  of  the  valley  of  the  Fair, 
and  that  of  the  Otter  west  of  Weybridge  village. 

East  of  the  Fair,  at  varying  distances  from  it,  the  surface 
rises  to  form  Weybridge  Hill,  which  is  a  ridge  of  much  the  same 
pattern  as  that  of  Snake  Mt.,  but  of  lower  elevation.  On  the 
west  of  the  ridge  are  steep  slopes  and  numerous  softened  scarps 
from  whose  summits  there  extends  eastward  an  irregular  surface 
which  in  general  descends  to  the  bed  of  Otter  Creek. 

Near  the  Cornwall  line  the  steep  western  margin  of  the 
ridge  forms  what  is  known  as  "The  Ledge."  It  is  marked  by  a 
scarp  which  extends  southward  into  Cornwall.  At  "The  Ledge" 
the  rock  is  massive,  gray  limestone  without  well-defined  structure 
or  dip.  It  yielded  no  fossils.  The  same  rock  continues  north- 
ward to  within  a  half  mile  of  Center,  a  small  settlement  two  miles 
south  of  Wevbridge  village. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  257 

Southwest  of  Center,  along  a  road  that  descends  diagonally 
across  the  steep  western  slope,  is  black  phyllite  forming  a  distinct 
s-carp,  to  the  west  and  east  of  which  lie  calcareous  rocks  much 
like  those  of  "The  Ledge."  The  phyllite  forms  the  northern 
termination  of  what  was  designated  in  the  Vermont  report  and 
by  later  observers  as  the  "central  belt  of  slate,"  and  has  been 
regarded  as  of  "Utica"  or  "Hudson  River"  age.  In  the  writer's 
opinion,  the  rock  has  little  resemblance  to  the  so-called  "Utica"  of 
the  lake  region  proper  and  does  not  suggest  an  altered  derivative 
of  that  formation.  On  the  contrary  it  is  entirely  similar  to  phyl- 
lite occurring  in  Cornwall  at  the  south,  which  will  be  described 
beyond,  and  which  seems  clearly  to  be  the  northward  extension 
of  the  phyllites  of  Whiting  and  Sudbury,  which  are  regarded  as 
much  older.  The  field  relations  southwest  of  Center  might  pos- 
sibly suggest  that  the  phyllite  is  interstratified  with  the  limestone 
that  borders  it  on  the  west  and  east;  but  such  relation  is  hardly 
possible  if  the  phyllite  is  what  the  writer  conceives  it  to  be.  The 
general  relations  point  to  displacements  and  it  seems  most  likely 
that  the  phyllite  was  thrust  into  the  limestone. 

North  of  Center  towards  Weybridge,  east  of  the  road,  is 
strongly  sheared,  calcareous  rock  of  quite  uncertain  correlation 
which  lies  to  the  west  of  numerous  outcrops  of  somewhat  marbly, 
dove-gray  limestone  associated  with  chamois-gray  patches  which 
are  badly  crumpled  and  mixed  up. 

Farther  north,  south  of  Weybridge  village,  what  now  appears 
as  massive,  gray,  dolomitic  limestone  forms  scarps  east  of  the 
road  to  Center.  The  rock  has  been  under  compression  but  is 
not  conspicuously  sheared.  No  fossils  were  found.  In  lithology 
it  resembles  somewhat  the  rock  at  "The  Ledge"  near  the  Corn- 
wall line  and  to  some  extent  also  the  gray  rock  that  is  found  at 
the  east  in  association  with  the  quartzite.  Similar  rock  forms 
the  falls  and  banks  of  the  river  at  Weybridge  village.  The  gray 
dolomite  at  Weybridge  village  is  on  the  meridians  of  that  which 
occurs  two  miles  north  of  the  village  in  New  Haven  and  the 
latter,  as  previously  shown,  with  slight  surface  interruption  joins 
the  interbedded  dolomites  and  quartzites  southeast  of  Buck  Mt. 

According  to  Dana,  Wing  found  at  Weybridge  upper  falls, 
on  the  west  side  of  the  slate,  presumably  the  northward  continua- 
tion of  the  phyllite  found  farther  south,  "Rhynchonella  beds" 
(called  Chazy)  lying  beneath  "Sparry  limestone"  (Trenton). 
The  "striped  stratum"  (Chazy)  was  described  as  full  of  fossils. 
This  locality  was  not  seen  by  the  writer,  but  became  known  to 
him  from  subsequent  reading  of  Mr.  Wing's  discoveries  in  Ver- 
mont. 

Southeast  of  Center,  on  the  road  towards  Middlebury  and 
in  adjacent  fields,  are  ledges  of  striped  limestone  which  suggest 
the  Chazy.  Farther  south  towards  Middlebury  along  the  road,  and 
over  the  part  of  the  township  lying  east  and  southeast  of  Center 


258  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

and  west  of  Otter  Creek,  are  abundant  ledges  of  sheared,  dark 
bluish  limestone  resembling  Trenton.  These  rocks  apparently 
occupy  a  broad  band  in  eastern  Weybridge,  west  of  Otter  Creek. 
Fossils  were  not  found  in  Weybridge.  Later,  on  a  trip  made 
over  territory-  southwest  of  Middlebury  village  in  northeastern 
Cornwall,  Trenton  fossils  were  found  in  similar  sheared,  dark 
bluish  limestones  which  lie  on  meridians  practically  marking  the 
western  boundary  of  the  similar  rocks  in  Weybridge. 

The  Otter  which  flows  north  from  Middlebury  village  forms 
part  of  the  eastern  boundary  of  Weybridge  and  separates  it  from 
Middlebury.  On  the  Middlebury  side  the  sheared,  bluish,  so- 
called  Trenton  rocks  give  place  to  marbly,  dull  gray  rocks  with 
associated  yellowish  or  chamois-gray  layers  which  form  a  broad 
band  in  this  part  of  Middlebury  township  and  join  at  the  north 
with  similar  rocks  in  the  southwestern  part  of  New  Haven,  which 
have  been  described. 

From  west  to  east  across  Weybridge  the  rocks,  broadly  speak- 
ing, are  not  disposed  in  folds,  but  in  an  irregular  sequence  prob- 
ably due  to  reverse  fault  displacements  along  the  strike,  with 
probably  some  imbrication  due  to  lateral  thrust.  The  latter  is 
not  clearly  exhibited  by  a  definite  contact  in  Weybridge,  but  in 
Middlebury  village  below  the  falls  a  good  overthrust  contact  may 
be  seen,  as  will  be  later  described. 

Middlebury  Township. 

(Middlebury   and   Brandon  topographic  sheets.) 

Location.  On  the  west  Middlebury  is  separated  from  Wey- 
bridge by  a  portion  of  Otter  Creek,  and  is  further  bounded  by 
a  part  of  Cornwall.  On  the  north  it  is  bounded  by  New  Haven 
and  a  part  of  Bristol,  on  the  east  by  Ripton,  and  on  the  south  by 
Salisbury.  The  eastern  portion  of  the  township  includes  a  strip 
along  the  western  border  of  the  Green  Mountain  plateau. 

General  description.  The  gray  limestones  and  interbedded, 
buff-  or  chamois-weathering  layers  which  lie  just  east  of  the 
Otter,  north  of  Middlebury  village,  have  already  been  mentioned. 
They  give  prominent  exposures  on  both  sides  of  the  railroad  track 
south  of  Beldens,  and  between  the  track  and  the  river  southward 
towards  Middlebury  village.  In  the  village  below  the  falls  they 
are  in  juxtaposition  with  strongly  sheared,  limy  shales  and  at 
one  place  show  a  good  thrust  contact,  with  the  shale  which  has 
been  pictured  by  Seely.  Seely  called  the  shale  Trenton  and  the 
overthrust  rock  Beekmantown. 

South  of  the  latitude  of  Beldens  these  rocks  continue  eastward 
at  the  surface  to  the  road  running  from  Middlebury  village  to 
New  Haven  Junction.  Southward,  west  of  Chipman  Hill  and 
east  of  the  railroad  track,  they  largely  pass  under  drift. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  259 

North  of  Chipman  Hill  a  cross  road  leaves  the  main  road 
Tjetween  New  Haven  and  Middlebury  and  runs  one-third  of  a 
mile  due  east  and  then  bends  southeastward.  South  of  this  road 
at  the  northern  end  of  Chipman  Hill  is  sheared  limestone  which 
corresponds  closely  with  rock  in  Ferrisburg  to  the  northeast  of 
the  city  of  Vergennes  and  which  near  Vergennes  by  the  fossils 
in  several  places  and  by  the  lithology  in  others,  was  correlated 
with  the  Chazy.  East  of  the  cross  road,  after  it  makes  it  bend 
to  the  southeast,  is  altered,  now  somewhat  crystalline  limestone, 
weathering  to  a  light  blue,  which  suggests  the  Trenton.  It  is 
apparently  without  fossils  at  this  place.  This  rock  is  on  the 
western  margin  of  a  ridge  which  extends  from  New  Haven  into 
Middlebury,  the  rocks  of  which  at  its  northern  end  in  New  Haven 
have  been  described  (page  249).  In  the  Middlebury  portion 
of  the  ridge,  west  of  the  road  that  runs  lengthwise  along  it,  is 
much  the  same  assemblage  of  rocks  found  at  the  northern  end. 
Rocks  identified  as  members  of  the  interbedded  series  of  dolomites 
and  quartzites  are  more  or  less  intermingled  with  outcrops  of 
striped  or  gray  limestone  and  some  gray  dolomite.  East  of  the 
road  are  abundant  exposures  of  gray  limestones  associated  with 
somewhat  yellowish-weathering  rocks.  These  sometimes  give 
place  to  striped  limestone  which  resembles  the  Chazy. 

Eastward  is  Muddy  Brook,  west  of  which  was  seen  quartzite 
associated  with  some  dolomite.  These  rocks  lie  on  a  meridian 
west  of  the  marble  at  "marble  ledge"  quarry  near  the  New 
Haven  line.  At  the  quarry  the  marble  is  associated  with  gray 
dolomite  which  forms  the  eastern  wall  of  the  quarry. 

East  of  Chipman  Hill  is  a  topographic  break  in  the  ridge 
mentioned  above.  South  of  this  break,  a  little  north  of  east  of 
Middlebury  village,  is  a  hill  of  camel-hump  shape  which  is 
geologically  a  southward  continuation  of  the  ridge.  This  hill 
presents  relations  of  much  interest.  On  the  top  of  the  hill  are 
interbedded  quartzites  and  dirty,  somewhat  yellowish-weathering 
dolomites,  dipping  westerly  and  not  strongly  sheared  or  folded, 
which  apparently  lie  on  bluish-gray  or  dull  gray  limestone  which 
seems  to  be  more  deformed  and  altered.  This  hill  seemed  to 
show  the  interbedded  rocks  of  probably  Lower  Cambrian  age 
resting  on  probably  younger  (Chazy)  limestone. 

South  of  this  hill  a  road  runs  from  Middlebury  village  east- 
ward towards  the  mountain.  The  road  forks  about  a  mile  east 
■of  the  village,  and  near  the  fork  gray  dolomite  is  seen  to  form  a 
fold  or  "roll"  very  much  like  the  structure  seen  at  the  old  quarry 
southeast  of  Leicester  Junction  and  at  the  Norcross  quarry  south 
of  Dorset  Mt.  One-half  mile  east  of  the  fork,  on  the  north 
side  of  the  road  running  east,  is  the  quarry  of  the  Middlebury 
Marble  Co.,  now  worked  for  lime.  The  marble  is  not  a  very 
good  commercial  stone,  but  in  all  essential  particulars  is  like  the 
marble  in  the  quarries  around  Brandon.     The  marble  continues 


260  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

eastward  for  a  short  distance  at  the  surface  and  then  gives  place 
to  gray,  siHceous  dolomite  and  interbedded  quartzite  and  dolomite, 
the  latter  dipping  easterly  at  a  high  angle.  The  dolomite  and 
interbedded  rocks  lie  along  meridians  occupied  both  to  the  north 
and  south  by  similar  rocks.  Eastward  is  other  gray  dolomite 
and  then  the  scarps  in  the  quartzite  along  the  edge  of  the  plateau. 

About  two  miles  south-southwest  of  Middlebury  village  are 
ledges  of  dove-gray  or  bluish  rock  which  were  regarded  as  prob- 
ably of  Chazy  age.  The  noteworthy  structure  is  the  strong 
shearing.  The  dip  is  obscure ;  in  some  places  it  seemed  to  be  to 
the  west ;  in  other  places  the  beds  appeared  to  stand  on  end. 
These  outcrops  are  a  mile  east-northeast  of  other  ledges  in  east- 
ern Cornwall  which  carry  Trenton  fossils,  including  Prasopora. 

Two  miles  directly  east  of  the  rocks  called  Chazy,  which  were 
just  mentioned,  and  south  of  the  road  from  Middlebury  village 
to  East  Middlebury,  are  two  short  ridges  composed  chiefly  of 
dove-gray  or  bluish  limestone  carrying  patches  of  yellowish-gray 
rock.  Similar  rocks  occur  one  and  a  half  miles  to  the  southwest, 
just  west  of  Otter  Creek  on  the  road  from  Farmingdale  to 
Cornwall. 

At  Farmingdale  are  outcrops  of  gray,  siliceous  dolomite  like 
that  usually  associated  with  the  quartzite  along  the  eastern  border 
of  the  lowland.  This  gray  dolomite  is  intermingled  with  some 
marbly  limestone  along  the  road  running  from  Farmingdale  east- 
ward to  within  a  fourth  of  a  mile  of  the  main  road  from  Salis- 
bury to  Middlebury.  West  of  East  Middlebury  village,  near  the 
junction  of  the  main  roads,  are  interbedded  dolomites  and  quartz- 
ites  forming  a  gentle  anticline,  the  beds  dipping  westerly  south 
of  the  road  from  East  Middlebury  to  Middlebury  on  one  meri- 
dian and  easterly  to  the  north  of  the  roads  on  a  meridian  slightly 
to  the  east  of  the  other. 

Along  the  road  from  East  Middlebury  to  Bristol,  a  mile 
northwest  of  East  Middlebury  village',  is  massive  quartzite  over- 
lain by  dolomite,  the  latter  clearly  dipping  westerly. 

In  the  bed  of  the  river  east  of  East  Middlebury  village,  beds 
of  quartzite  dip  westerly. 

South  of  East  Middlebury  is  a  hill  composed  of  granular, 
gray  quartzite  which  is  a  dismembered  part  of  the  rock  of  the 
plateau. 

The  geological  relations  and  topographic  features  in  the  east- 
ern part  of  Middlebury  township  are  very  similar  to  those  found 
at  many  places  along  the  eastern  edge  of  the  lowland  and  in  the 
Vermont  valley.  They  are  in  all  cases  apparently  of  similar 
genesis.  The  rocks  in  the  eastern  part  of  the  lowland  are  dis- 
membered parts  of  the  formations  of  the  plateau. 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  261 

Bridport  Township. 

(Port  Henry  and  Ticonderoga  topographic  sheets.) 

Location.  Bridport  borders  the  lake  and  Hes  south  of  Addi- 
son. It  is  bounded  on  the  east  by  parts  of  Weybridge  and  Corn- 
wall and  on  the  south  by  Shoreham. 

General  description.  Away  from  the  lake  shore  in  the  west- 
ern part  and  over  the  central  portions  of  Bridport,  clay  usually 
conceals  the  hard  rock.  Outcrops  of  shale  yielding  broken  grap- 
tolites  outcrop  intermittently  along  shore  from  a  point  near  the 
northern  township  line  southward  past  Plumies  Point  to  a  con- 
spicuous jog  in  the  shore  line  about  one  and  a  half  miles  north  of 
Crown  Point  ferry  landing. 

Near  the  landing  at  West  Bridport  are  what  appear  to  be 
Chazy  and  Black  River  beds. 

Seely  mentioned  some  exposures  of  so-called  Beekmantown 
rocks  near  the  head  of  the  West  Branch  of  Dead  Creek ;  but  on 
his  map  showed  such  rocks  at  the  head  of  the  East  Branch.  The 
writer  did  not  see  these  rocks,  but  found  flat,  clay-covered  land 
around  the  head  of  the  West  Branch.  Southward  in  .Shoreham, 
shales  outcrop  on  meridians  occupied  by  the  We'st  Branch  in 
Bridport. 

Shales  outcrop  north  and  south  of  Bridport  village  and  at 
places  along  the  road  which  runs  east  from  the  main  Bridport- 
Addison  road  just  north  of  the  village.  Along  the  second  road 
running  east,  north  of  the  village,  about  two  miles  east  of  the 
Addison  road,  and  on  the  meridians  of  the  Red  Sandrock  to  the 
north  in  Addison,  are  blackish  shales  which  sometimes  are  strong- 
ly folded  and  sometimes  lie  rather  flat,  all  marked  by  well-de- 
veloped cleavage.  Southwestward  these  rocks  give  place  at  the 
surface  to  sheared,  shaly  limestone  and  these  in  turn  to  some- 
what m3.ssive,  plainly  bedded  limestone,  which  is  not  severely 
deformed  internally  and  which  has  much  the  aspect  of  other  rock 
a  mile  to  the  southwest  which  is  clearly  older  than  the  shale.  The 
shale  is  a  mile  slightly  to  the  west  of  south  of  the  southward  ex- 
tension of  the  Red  Sandrock  of  Weybridge  into  the  northeastern 
part  of  Bridport. 

South  of  Bridport  village  a  road  runs  easterly,  to  the  north 
of  Hemenway  Hill.  Along  this  road  and  south  of  it  in  the  field 
are  blackish  cleaved  shales,  which  a  mile  east  of  the  main  Brid- 
port-Shoreham  road  are  succeeded  along  the  road  by  thinly- 
bedded,  blue  limestone  with  good  Trenton  fossils.  East  of  these 
Trenton  beds  a  road  runs  southerly  on  the  east  side  of  Hemenway 
Hill.  West  of  this  road  and  just  south  of  the  fossiliferous  Tren- 
ton outcrops  are  ledges  of  rock  which  nn  its  lithology  suggests 
part  of  the  Beekmantown  in  Shoreham.  Farther  south  on  the 
east  slope  of  the  hill  are  outcrops  of  rock  of  more  decfded  re- 
semblance to  some  of  the  Beekmantown.     The  beds  dip  to  the 


262  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

east  and  are  on  meridians  occupied  by  beds  correlated  with  the 
Beekmantown  at  Mutton  Hill  in  Shoreham. 

The  rocks  outcropping  on  the  east  slope  of  Hemenway  Hill 
are  separated  by  the  flat  land  along  the  Lemon  Fair  River  from 
rocks  forming  a  low  ridge  in  western  Cornwall  and  which  appear 
to  be  the  northern  continuation  of  the  rocks  of  Cutting  and  Delano 
Hills  in  Shoreham.  which  are  considered  to  be  of  Beekmantown 
age,  as  defined  by  Brainerd  and  Seely. 

The  conditions  in  the  eastern  part  of  Bridport  certainly 
strongly  suggest  upthrust  of  older  rocks  into  younger  ones,  with 
some  overlap  of  the  former.  The  older  rocks  are  in  some  cases 
members  of  the  Red  Sandrock  series  and  in  others  probably  of 
the  Beekmantown.  Probably  Chazy  and  Trenton  beds  have  in 
some  cases  been  involved  in  thrust. 

Cornwall  Township. 

(Port  Henry,  Ticonderoga,  Middlebury  and  Brandon  topographic 

sheets.) 

Location.  Cornwall  on  the  west  adjoins  the  southeastern 
part  of  Bridport  and  the  northeastern  part  of  Shoreham.  It  is 
bounded  on  the  north  by  Weybridge,  on  the  east  by  parts  of  Mid- 
dlebury and  Salisbury,  and  on  the  south  by  Whiting. 

General  description.  The  red  quartzite  of  the  Red  Sandrock 
series  of  the  Snake  Mt.  mass  projects  from  Bridport  and  Wey- 
bridge into  the  northwestern  part  of  the  township. 

On  the  meridians  of  this  quartzite,  farther  south  along  the 
western  border  of  the  township,  is  a  ridge  falling  off  on  the  west 
into  the  flat  land  along  the  Lemon  Fair  in  southeastern  Bridport, 
and  sloping  more  gradually  eastward  into  more  or  less  drift- 
covered  land.  The  rock  in  the  ridge  has  been  called  Beekman- 
town and  certainly  has  resemblance  to  part  of  that  formation  as 
described  for  Shoreham.  The  dip  is  apparently  generally  if  not 
always  to  the  east. 

East  of  Beaver  Branch  rises  another  ridge  of  somewhat 
similar  pattern  which  is  the  southward  extension  from  Weybridge 
into  Cornwall  of  the  ridge  already  described  for  its  northern  por- 
tion in  Weybridge.  Its  western  margin  begins  at  the  north  in  a 
precipitous  scarp  known  as  "The  Ledge."  The  scarp  continues 
southward  for  a  distance  of  two  miles  and  merges  with  a  more 
gentle  slope  northwest  of  CQrnwall  village.  The  beds  dip  east- 
erly. The  rock  may  be  largely  Beekmantown,  but  about  a  half 
mile  northwest  of  Cornwall  village  are  beds  of  dove-gray  rock 
also  dipping  easterly  and  apparently  stratigraphically  above  the 
rocks  to  the  northwest  of  them.     These  beds  may  be  Chazy. 

Outcrops  of  Chazy  limestone,  which  in  some  places  show 
fossils,  occur  south  of  the  village  along  the  road  towards  Whiting. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  263 

These  rocks  are  succeeded  southward  by  exposures  of  sheared 
limestone  of  uncertain  correlation. 

The  main  road  going  north  from  Cornwall  village  forks 
about  a  mile  and  a  half  north  of  the  village.  Along  the  west 
branch,  near  the  fork  of  the  road,  is  black  phyllite.  Just  east  of 
this  rock  are  ledges  of  sheared  limestone  which  gave  good  Tren- 
ton fossils,  as  previously  described  (page  258).  The  Trenton 
rocks  continue  southward  to  the  east  of  the  road  through  Corn- 
wall village  and  are  intermingled  with  black  phyllite  or  schist 
carrying  some  massive  quartzite. 

One-third  of  a  mile  north  of  the  village  a  road  runs  easterly 
towards  Farmingdale  in  Middlebury.  Two-thirds  of  a  mile  east 
of  the  main  road  are  ledges  of  quartzite  with  associated  black 
phyllite  which  are  succeeded  easterly  by  ledges  of  limestone  re- 
sembling the  Trenton.  Fossils  were  not  found.  Eastward  are 
beds  of  sheared  rock  resembling  the  Chazy.  These  presumably 
Chazy  beds  form  a  short,  low  ridge  along  the  western  border  of 
the  northern  end  of  Cedar  Swamp ;  the  beds  dip  easterly  and  carry 
obscure  fossils. 

Near  the  Whiting  line  a  road  runs  easterly  from  the  main 
Whiting-Cornwall  road  towards  Salisbury  station.  Black  phyl- 
lite outcrops  along  this  road  and  in  the  fields  north  of  it,  to  the 
west  of  Cedar  Swamp.  Observations  showed  that  the  black 
phyllite  or  schist  is  frequent  north  of  this  road,  between  the 
swamp  and  the  Whiting-Cornwall  road.  It  is  associated  with 
sheared  limestone  of  uncertain  correlation. 

Black  phyllite  was  also  found  along  the  road  running  west 
from  Middlebury  village,  about  two  and  a  half  miles  west  of  the 
village  and  a  mile  south  of  the  Weybridge  line.  This  phyllite 
joins  that  of  Cornwall  with  that  of  Weybridge. 

The  relations  northeast,  east  and  southeast  of  Cornwall 
village  are  strikingly  similar  to  those  found  at  the  northern  end 
of  the  Taconic  range  in  Sudbury,  except  that  in  Cornwall  there 
is  less  quartzite  exposed  and  more  phyllite  mingled  with  the  cal- 
careous rocks  than  is  the  case'  in  Sudbury,  and  that  the  calcareous 
rocks  carry  obscure  fossils  in  Cornwall  and  in  other  respects  seem 
to  be  more  easily  recognized.  The  phyllites  of  Cornwall  join 
through  the  similar  rocks  of  Whiting  with  the  quartzites  and 
schists  of  Sudbury. 

In  the  early  descriptions  of  the  black  and  lighter  colored 
phyllites  and  the  quartzites  which  extend  north  from  Sudbury 
through  Whiting  and  Cornwall  into  Weybridge  they  were  re- 
garded as  of  "Utica"  (Brainerd  and  Seely)  or  "Hudson  River" 
(Vermont  Report,  Wing  and  Dana)  age.  The  principal  reason 
for  such  assignments  seems  to  have  been  because  they  are  asso- 
ciated with  rocks  of  Trenton  age,  which  are  intermingled  with 
them  or  border  them. 


264  REPORT  OF  THE  VERMONT'  STATE  GEOLOGIST. 

The  Vermont  Report  and  Wing  both  recognized  that  the 
"central  belt  of  slate"  in  Weybridge,  Cornwall  and  Whiting  is  the 
northern  continuation  of  the  Taconic  range;  but  apparently 
neither  considered  the  possibility  that  the  rocks  composing  it  may 
be  much  older  than  they  indicated. 

It  has  already  been  remarked  that  the  phyllite  of  Weybridge 
bears  little  resemblance  to  the  rocks  near  the  lake.  The  quartzite 
occurring  with  the  phyllite  in  Cornwall  and  Whiting  in  such  way 
as  to  leave  no  doubt  of  the  common  membership  of  the  two  in 
one  formation  seems  to  prohibit  the  inclusion  of  these  rocks  with 
the  Ordovician  shale.  On  the  other  hand,  the  phyllite  and  quartz- 
ite are  so  similar  to  rocks  in  the  Taconic  range  and  at  some  places 
along  the  western  margin  of  the  plateau  near  Brandon  that  they 
probably  belong  to  the  same  formation  and  to  one  including  the 
granular  quartzite,  and  are  probably,  therefore,  of  Lower  Cam- 
brian age. 

There  may  also  be  said  to  be  some  doubt  as  to  the  inclusion 
of  all  the  gray,  dolomitic  limestone  that  occurs  to  the  east  of  the 
Red  Sandrock  of  Snake  Mt.  in  northern  Cornwall,  but  particu- 
larly in  Weybridge,  in  the  Lower  Ordovician  (Beekmantown). 
On  a  lithological  basis,  which  is  often  the  only  one  that  may  be 
employed,  it  would  be  hard  to  decide ;  for  some  of  the  gray  rock 
is  siliceous  and  has  much  the  same  appearance  as  the  rock  asso- 
ciated with  quartzite  nearer  the  plateau.  The  matter  is  com- 
plicated not  only  by  undoubted  deformations,  but  probably  also 
by  unusual  conditions  of  sedimentary  overlap  of  Ordovician  beds 
on  an  eroded  surface  of  Cambrian  rocks  which  included  siliceous 
dolomite,  as  has  been  frequently  shown. 

Shoreham  Township. 

(Ticonderoga  and  Brandon  topographic  sheets.) 

Location.  Shoreham  lies  south  of  Bridport  and  is  bordered 
on  the  west  by  the  lake,  on  the  east  by  parts  of  Cornwall  and 
Whiting,  and  on  the  south  by  Orwell. 

General  description.  In  his  first  paper  the  writer  briefly  dis- 
cussed certain  features  of  the  geology  of  this  township,  based 
upon  a  personal  review  of  the  geological  relations  described  by 
Brainerd  and  Seely,  and  in  connection  with  the  geology  of  the 
town  of  Orwell  which  adjoins  Shoreham  on  the  south.  The  east- 
ern part  of  the  township  displays  the  type  section  of  the  so-called 
Beekmantown  of  western  Vermont.  For  a  detailed  description 
of  this  section  the  reader  is  referred  to  Brainerd  and  Seely's 
original  account.^ 

What  underlies  the  flat  land  along  the  course  of  the  Lemon 
Fair  River  in  southeastern  Bridport  may  only  be  conjectured ; 
but  immediately  east  of  this  flat  area  in  Cornwall  and  south  of  it 

iBull.  No.  3,  Arner.  Mus.  Nat.  Hist.,  1890-91. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  265 

in  Shoreham  are  rocks  which  by  comparison  with  those  of  the 
East  Shoreham  section  are  apparently  to  be  correlated  with  the 
so-called  Beekmantown.  In  the  very  northeastern  part  of  the 
township  the  Lemon  Fair  has  trenched  these  rocks  and  low  cliffs 
appear  in  them  on  both  sides  of  the  stream.  On  the  east  side, 
practically  on  the  Cornwall  line,  and  on  the  road  running  west 
from  West  Cornwall  village,  a  steep  westerly  dip  was  noted  and 
the  beds  are  sheared  across  the  bedding.  From  these  ledges  a 
scarp  runs  southward  along  the  western  base  of  the  hill  and  the 
prevailing  dip  along  it  is  apparently  to  the  east.  About  two-thirds 
of  a  mile  south  of  the  westerly-dipping  beds  some  Chazy  appears 
to  be  present  on  the  west  side  of  the  road.  Southward  along  the 
old  "Amherst  road"  to  Richville  what  appear  to  be  Beekmantown 
rocks  may  be  followed  by  intermittent  outcrops  showing  easterly 
dip  nearly  to  Richville.  The  rocks  along  this  road  are  the  north- 
ern extension  of  those  of  Delano  and  Cutting  Hills  which  are 
included  in  Brainerd  and  Seely's  Shoreham  section  of  the 
Beekmantown. 

Observations  show  that  the  eastern  half  of  Shoreham  town- 
ship is  largely  formed  of  Beekmantown  which  is  associated  with 
some  older  rocks  of  so-called  "Potsdam"  age  and  younger  beds 
belonging  to  the  Chazy  and  Trenton.  Chazy  and  Trenton  beds 
border  the  Beekmantown  on  the  east  and  are  involved  with  it 
just  east  of  Shoreham  village.  As  Brainerd  and  Seely  clearly 
showed,  the  massive  rocks^  have  been  broken  by  thrust  faults 
along  the  general  strike  of  the  rocks  at  several  places.  By  these 
thrusts  the  older  Beekmantown  and  underlying  "Potsdam"  have 
been  fractured  so  that  older  beds  have  moved  into  and  over 
younger  rocks.  Prior  to  or  during  thrusting,  some  folding  oc- 
curred ;  but  the  major  deformation  was  that  of  fracture  accom- 
panied by  thrusting. 

At  Mutton  Hill,  two  miles  north  of  Shoreham  village,  massive 
teds  of  quartzite  of  so-called  "Potsdam"  age  dip  easterly  on  the 
west  side  of  the  hill  and  appear  to  pass  conformably  beneath 
Beekmantown  beds  which  also  dip  easterly.  Southeast  of  Mutton 
Hill  quartzite  and  dolomitic  limestone  show  the  effect  of  great 
pressure  and  at  some  places  have  easterly  dip. 

The  "Potsdam"  quartzitic  sandstone  and  overlying  Beek- 
mantown may  be  followed  south  from  Mutton  Hill  through 
Shoreham  village  to  Barnum  Hill  near  the  Orwell  line  and  then 
into  Orwell,  where  the  marginal  trace  of  the  overthrust  rocks  may 
be  seen  north  of  Huff's  Crossing. 

West  of  Shoreham  village,  at  Sisson  Hill  and  west  and  north- 
west of  it,  and  along  the  road  from  Larrabee's  Point  to  Cream 
Tlill  are  abundant  exposures  of  the  black  Ordovician  shales,  often 
folded,  but  sometimes  lying  nearly  flat,  and  always  sheared. 
These  shales  show  practically  the  same  structural  features  as 
those  which  have  been  described  in  previous  pages.     It  has  be- 


266  REPORT  OP  THE  VERMONT  STATE  GEX)LOGIST. 

come  evident  that  the  shales  hold  throughout  a  long  distance  in 
western  Vermont  to  much  the  same  structural  features.  Near 
the  margins  of  overthrust  they  are  always  excessively  jammed 
and  sheared,  but  may  nevertheless  often  retain  a  flattish  attitude, 
having  undergone  their  chief  deformation  by  shearing. 

The  shales  outcrop  at  Fivemile  Point  and  southward  along 
the  lake  shore,  but  in  northwestern  Shoreham  the  area  inter- 
vening between  the  shore  and  the  road  running  north  from  Lar- 
rabee's  Point  is  covered  by  the  ubiquitous  clay. 

East  of  Cream  Hill  is  Cedar  Swamp,  which  separates  the 
shales  of  Cream  Hill  from  the  "Potsdam"  and  Beekmantown  of 
Mutton  Hill.  Shales  presumably  underlie  most  of  the  area  of 
the  swamp,  which  marks  a  zone  of  displacement. 

Near  Larrabee's  Point,  north  of  the  boat  landing,  are  Tren- 
ton beds  in  association  with  shales  and,  south  of  the  landing,. 
Trenton  beds  are  underlain  by  others  of  Black  River  age  and 
these  by  gray  limestone  of  uncertain  correlation. 

In  Shoreham  the  evidence  for  reverse  faulting  and  thrust- 
ing is  clear  and  distinct.  It  is  even  more  so  in  Orwell  at  the 
south,  as  the  writer  has  elsewhere  shown. 

Whiting  Township. 

(Brandon  topographic  sheet.) 

Location.  This  township  lies  directly  south  of  Cornwall.  It 
is  bounded  on  the  west  by  parts  of  Shoreham  and  Orwell,  on  the 
east  by  parts  of  Salisbury  and  Leicester  and  on  the  south  by  Sud- 
bury. 

General  description.  For  Whiting  a  brief  description  will 
suffice.  The  hard  rocks  are  concealed  by  surface  material  over 
much  of  its  area,  particularly  in  the  eastern  portion  to  the  west 
of  Otter  Creek.  As  already  mentioned,  the  phyllites  extend 
north  from  Sudbury  through  the  central  part  of  Whiting.  In 
the  northwestern  part,  limestone  of  apparently  Trenton  age  bor- 
ders the  band  of  phyllite  on  the  west.  In  the  southeastern  part 
along  and  near  the  road  running  from  Whiting  village  to  Leicester 
Junction  and  also  south  of  this  road  are  more  or  less  detached 
exposures  of  limestone  which  seems  to  be  the  northern  continua- 
tion of  sheared,  marbly  and  bluish  limestone  carrying  layers  and 
patches  of  yellowish-weathering  rock  which  make  up  the  con- 
spicuous hills  in  the  northeastern  part  of  Sudbury.  Eastward, 
these  rocks  join  with  others  that  are  similar  in  the  western  part 
of  Leicester. 

Salisbury  Township. 

(Brandon  topographic  sheet.) 

Location.  The  western  boundary  is  formed  by  a  portion  of 
Otter  Creek,  which  separates  the  township  from  parts  of  Corn- 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  267 

wall  and  Whiting.  It  is  bounded  on  the  north  by  Middlebury, 
on  the  east  by  parts  of  the  mountain  towns  of  Ripton  and  Goshen, 
and  on  the  south  by  Leicester. 

General  description.  The  western  portion  between  Otter 
Creek  and  the  railroad  track  is  low,  flat  land  and  affords  few  out- 
crops. West  of  Salisbury  station,  in  the  lowland  that  borders 
Otter  Creek,  are  a  few  island-like  knolls  of  marbly  or  bluish 
limestone  with  layers  of  chamois  or  pinkish-buff  color.  The 
rocks  frequently  show  thinly  laminated  structure.  The  whole 
assemblage  is  much  like  that  found  southward  in  Leicester  and 
in  the  northeastern  part  of  Sudbury  and  adjoining  parts  of 
Whiting. 

A  road  runs  south  from  Salisbury  station,  just  to  the  east 
of  the  railroad  track.  East  of  this  road  and  a  few  rods  south  of 
the  station,  dove-blue  or  marbly  limestone,  often  with  thinly- 
laminated  structure  that  represents  or  simulates  bedding,  is  asso- 
ciated with  chamois  or  pinkish-buff  colored  beds  and  the  two  give 
an  assemblage  that  is  very  much  like  that  found  in  the  hills  in 
the  northeastern  part  of  Sudbury.  The  structure  is  often  much 
like  that  found  among  the  interbedded  quartzites  and  dolomites 
lying  to  the  east;  at  places  beds  which  have  been  closely  folded 
and  now  stands  on  end  lie  against  others  forming  a  gentle  syncline. 
Between  such  compressed  zones  and  the  less  violently  folded 
rocks  there  apparently  exists  a  displacement  due  to  reverse  fault- 
ing. These  rocks  continue  southward.  A  mile  south  of  the 
station,  south  of  a  cross  road  running  east,  in  some  outcrops  of 
westerly-dipping  beds  which  appeared  to  be  conformable,  bluish, 
marbly  limestone  is  interbedded  with  chamois  colored  rock  and 
these  are  apparently  underlain  by  interbedded  marble,  chamois- 
gray  limestone  and  quartzite,  the  latter  usually  in  thin  beds  but 
showing  one  about  a  foot  thick. 

Two-thirds  of  a  mile  to  the  southeast  of  these  outcrops  is  a 
hill  in  which  the  rock  on  the  west  slope  and  part  of  the  summit  is 
marbly,  dove-blue  rocks  showing  extreme  effects  of  pressure 
which  is  expressed  by  conspicuous  flow  and  fracture  shearing. 
At  the  summit  of  the  east  slope  of  this  hill  are  patches  of  quartz- 
ite which  seemed  either  to  rest  on  the  sheared,  marbly  rocks  or  to 
be  involved  with  them  by  thrust. 

On  the  meridian  of  these  rocks,  about  a  mile  south  of  West 
Salisbury  village  and  east  of  the  road  running  south  from  it,  is 
another  hill  on  the  northwestern  side  of  which  are  many  outcrops 
of  striped  blue  rock,  strongly  resembling  the  Chazy  of  the  lake 
region.  The  beds  have  prevailingly  westerly  dip,  but  are  strongly 
sheared  with  easterly  dipping  cleavage.  No  fossils  were  found. 
A  cross  road  skirts  this  hill  on  the  south  and  runs  easterly  to 
join  the  Farmingdale-Salisbury  road.  Along  the  cross  road,  to 
the  east  of  the  hill,  is  gray,  siliceous  dolomite  like  that  associated 
with  the  quartzite  along  the  eastern  edge  of  the  lowland.     A  few 


268  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

rods  east  of  this  dolomite  is  marble,  then  more  gray  dolomite 
dipping  easterly,  then  east  of  the  Farmingdale  road  the  inter- 
bedded  series  of  quartzite  and  dolomite  which  forms  an  anticline 
between  the  Farmingdale  road  and  the  one  that  runs  northward 
from  Salisbury  village  on  the  west  of  Sunset  Hill. 

From  descriptions  just  given,  it  will  be  apparent,  by  reference 
to  the  writer's  first  paper,  that  northwest  of  Salisbury  village, 
marble,  gray  dolomite  and  interbedded  dolomites  and  quartzites 
are  involved  in  field  relations  quite  like  those  which  occur  around 
Brandon. 

West  and  north  of  Lake  Dunmore,  quartzite.  siliceous  dolo- 
mite and  interbedded  quartzites  and  dolomites  have  such  field 
relations  to  one  another  as  to  leave  no  doubt,  even  in  their  present 
disturbed  and  eroded  condition,  of  their  common  membership 
in  one  formation.  To  what  extent  these  different  rocks  may 
grade  laterally  into  one  another  the  conditions  in  the  eastern  part 
of  Salisbury  do  not  permit  statement.  As  has  been  elsewhere 
shown,  at  some  places  in  the  Vermont  valley  the  vertical  sequence 
is  more  or  less  plainly  from  basal  quartzite  through  gray  dolomite 
into  interbedded  quartzites  and  dolomites. 

East  of  Lake  Dunmore  is  a  very  prominent  scarp  of  quartzite 
forming  the  western  edge  of  the  plateau.  Dolomite  resting  on 
quartzite  occurs  above  this  scarp  around  Silvef  Lake.  It  also 
occurs  at  places  around  the  shore  of  Lake  Dunmore  in  such  rela- 
tions as  to  indicate  that  normally  the  dolomite  rests  on  quartzite. 
The  rocks  around  Dunmore  and  north  of  it  are  in  fact  more  or 
less  completely  dismembered  portions  of  the  plateau. 

A  section  from  Lake  Champlain  eastward  through  Shore- 
ham,  Whiting  and  Salisbury  to  the  Green  Mountain  plateau  is 
comparable  with  one  farther  south  extending  from  the  lake  east- 
ward through  Orwell,  Sudbury  and  Brandon.  The  essential 
similarity  is  disguised  but  not  obscured  by  differences  in  degree 
of  displacement  of  the  rocks.  The  northern  section  is  a  down- 
throw region  in  relation  to  the  other,  partly  from  flexure  in  the 
direction  of  the  strike  and  partly  from  faulting,  due  in  part 
probably  to  deformation  subsequent  to  earlier  thrust  displace- 
ments. It  should  again  be  noted,  perhaps,  that  it  will  apparently 
always  be  difficult  to  discriminate  between  displacements  primarily 
resulting  from  pressure  and  those  which  were  caused  by  normal 
faulting  either  along  independent  planes,  or  along  those  of  earlier 
thrusting. 

In  the  northern  section  the  younger  rocks  (Ordovician)  are 
more  fully  preserved  and  apparently  show,  in  spite  of  deforma- 
tion, an  overlapping,  probably  disconformable,  depositional  series 
ranging  from  the  "Potsdam"  (Ozarkian)  through  "Beekman- 
town,"  Chazy  and  Trenton.  Thrusting  has  partly  restored  the 
ancient  Cambrian  surface  on  which  these  rocks  were  laid  down. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  269 

In  the  southern  section  the  Cambrian  is  more  fully  shown  (see 
writer's  first  paper). 

Leicester  Township. 

(Brandon  topographic  sheet.) 

Location.  Leicester  lies  south  of  Salisbury.  It  is  separated 
by  a  portion  of  Otter  Creek  from  Whiting  on  the  west  and  is 
bounded  on  the  south  by  Brandon  and  on  the  east  by  Goshen. 

General  description.  The  rocks  of  this  township  join  those 
of  Salisbury  with  those  of  Brandon.  They  present  practically 
nothing  that  is  essentially  different  in  respect  to  rock  type  or 
structure  from  the  areas  to  the  north  and  south. 

The  ledges  in  southern  Salisbury  are  separated  from  out- 
crops in  southern  Leicester  by  the  wooded  flats  or  swampy  land 
along  Leicester  River  and  its  tributaries. 

In  the  Huntley  lime  quarry,  west  of  the  Otter  at  Leicester 
Junction  and  west  of  the  main  quarry  at  some  smaller  holes, 
may  be  seen  buff  and  pinkish  colored  beds  of  marble  or  crystal- 
line limestone,  usually  standing  at  a  high  angle  of  dip.  At  the 
big  quarry  these  beds  are  jammed  in  with  gray  dolomite  and  all 
show  the  effects  of  extreme  compression;  but  none  of  the  rocks 
indicates  much  in  any  respect  as  to  its  age. 

At  the  so-called  Swinnington  quarry,  southeast  of  the  Junc- 
tion and  east  of  the  Otter,  marbly  limestone  which  has  been  quar- 
ried is  overlain  by  gray,  magnesian  rock  which  shows  a  remark- 
able fold  in  the  form  of  a  recumbent,  closely  compressed  anticline 
which  has  been  aptly  called  a  "roll."  This  is  pictured  by  the 
State  Geologist  (Seventh  Report,  p.  352).  The  roll  is  inter- 
preted by  the  writer  as  the  portion  of  a  mass  now  largely  eroded 
which  was  thrust  over  the  marble  on  which  it  now  rests.  The 
peculiarly  folded  structure  was  probably  acquired  by  frictional 
drag  during  thrust.  Similar  rolls  have  been  mentioned  in  pre- 
vious pages  for  other  places  ^  in  western  Vermont  at  which  ap- 
parently similar  rocks  were  involved. 

Two-thirds  of  a  mile  east  of  the  Junction,  north  of  the  road 
running  east  from  the  covered  bridge,  are  ledges  of  dove-blue  or 
marbly  limestone  v/ith  patches  of  chamois-gray.  Eastward  these 
pass  under  drift;  but  about  a  mile  to  the  east  are  ledges  of 
strongly  sheared,  striped,  blue,  crystalline  limestone  not  very 
distant  from  others  of  gray,  siliceous  dolomite  like  that  which  is 
associated  with  the  quartzite  at  the  east.  East  of  these  are  other 
ledges  of  dove-blue  limestone  and  its  associated  chamois-gray 
rocks  and  farther  east  the  interbedded  dolomites  and  quartzites 
which  are  much  folded  and  form  the  southward  continuation  of 
the  similar  rocks  of  Salisbury  and  the  northern  extension  of  those 
in  Brandon.  The  interbedded  rocks  extend  in  Leicester  to  the 
east  of  Mt.  Pleasant,  which  is  bordered  on  the  east  by  a  distinct 
scarp,  at  the  base  of  which  lies  Mud  Pond. 


270  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

Lake  Dunmore  lies  in  a  structural  basin  perhaps  primarily  of 
synclinal  structure,  but  bounded  on  the  west  and  east  by  faults. 
Those  on  the  east  are  the  southern  extension  of  those  marking" 
the  western  edge  of  the  plateau  in  Salisbury. 

In  some  particulars  the  interbedded  rocks  of  Leicester  form 
a  transition  between  those  found  farther  south  in  the  Vermont 
valley  and  those  occurring  over  the  eastern  portions  of  the  low- 
land in  the  northern  townships.  This  transitional  character  is 
shown  by  thicker  beds  and  by  reddish  colors  which  are  more 
common  at  the  north. 

GENERAL  SUMMARY. 

Edward  Hitchcock  in  his  "Preliminary  Report,"  a  sort  of 
preface  to  the  first  volume  of  the  Geology  of  Vermont,  wrote  in 
substance  that  the  rocks  of  Vermont  were  the  most  difficult  ones 
to  understand  of  any  with  which  he  had  ever  attempted  to  grap- 
ple. It  does  not  appear  in  his  remark  whether  he  drew  any 
distinctions  among  the  different  rocks ;  but  apparently  he  recog- 
nized that  although  the  geology  of  some  parts  of  the  state  is 
easier  to  comprehend  than  that  of  other  parts,  the  whole  region 
is  one  of  great  complexity.  The  efforts  of  many  workers  have 
contributed  only  to  a  partial  solution  of  the  age  relations  and  struc- 
tural features  of  the  various  rocks. 

In  the  lake  region  proper,  as  defined  in  this  paper,  fossils 
were  found  many  years  ago  and  the  ages  of  the  different  rocks 
are  now  for  the  most  part  at  least  approximately  known ;  but  their 
structural  relations  have  always  been  and  are  even  now  obscure. 
While  distinct  progress  has  been  made  by  Wing  and  others  in 
tracing  the  formations  of  the  lake  region  into  the  eastern  parts  of 
the  Champlain  lowland,  the  Vermont  valley  and  the  Taconic 
range,  it  has  not  seemed  altogether  strange  that  Hitchcock  was 
confounded  by  the  obscurity  which  prevails  over  the  areas  which 
he  mapped  as  "Eolian  Limestones,"  in  which,  metamorphism  and 
deformation  have  introduced  so  much  confusion. 

It  is  not  the  purpose  of  this  summary  to  point  out  in  detail 
how  the  writer's  views  differ  from  those  of  others ;  but  it  seems 
as  though  confusion  has  often  resulted  from  failure  to  interpret 
correctly  the  major  structural  features  of  the  region. 

For  the  sake  of  convenience  of  discussion,  western  Vermont 
may  again  be  broadly  defined  as  that  part  of  the  state  which  in- 
cludes the  islands  of  the  lake  and  the  low  areas  along  its  borders, 
herein  called  the  lake  region  proper,  the  relatively  low  land  lying 
between  the  lake  region  and  the  Green  Mountain  plateau,  the 
western  marginal  portion  of  the  plateau,  the  Vermont  valley  and 
the  Taconic  range.  These  various  divisions  together  form  a  fairly 
broad  region  east  of  the  New  York  boundary,  reaching  across  the 
state  from  north  to  south. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  271 

The  writer  started  out  on  the  program  of  surveying  this 
whole  region.  The  work  has  been  accomphshed,  after  a  fashion, 
for  the  Vermont  valley  and  the  Champlain  lowland  and  for  parts 
of  the  Taconic  range  and  the  western  margin  of  the  plateau. 
The  survey  as  made  has  hardly  been  exhaustive,  but  has  been 
carried  out  as  carefully  as  possible  in  the  time  that  has  been  avail- 
able for  the  purpose.  Experience  has  served  to  show  how  puz- 
zling are  the  problems  presented  by  the  region  and  how  elusive 
is  any  final  and  definite  solution  of  some  of  them.  However,  in 
spite  of  the  difficulties  that  stand  in  the  way  and  the  uncertainties 
that  exist,  there  seem  to  be  manifest  such  similarities  among 
various  rocks  and  in  the  field  relations  shown  by  them  that  some 
generalizations  may  be  ofifered  which  would  hardly  be  warranted 
without  a  survey  of  the  region  as  a  whole. 

When  the  various  outcrops  that  have  been  described  in  the 
preceding  pages  have  been  plotted  on  the  several  topographic 
sheets  involved  and  these  are  placed  in  their  proper  positions  with 
respect  to  each  other,  certain  features  and  field  relations  stand 
out  which  now  deserve  examination  and  discussion. 

In  the  first  place  it  becomes  very  evident  that  the  major 
physiographic  features  and  many  of  the  minor  ones  as  well  are 
primarily  due  to  ancient  deformations  of  the  rocks  which  set  the 
stage  for  later  structural  changes  and  the  action  of  erosive  agents. 
The  various  divisions  which  have  been  defined  are  all  structurally 
homologous  areas,  some  more  obviously  than  others,  which  are  at 
the  present  time  largely  separable  only  on  geographic  and  physi- 
ographic bases.  This  homology  consists  in  the  essentially  identical 
types  of  rocks  found  in  each  and  the  major  structural  relations 
which  these  formations  have  to  each  other.  While  the  writer's 
studies  in  the  Taconic  range  lack  the  measure  of  fullness  of  those 
carried  out  in  the  lowland  divisions,  it  seems  most  probable  that 
this  division  is  only  a  special  physiographic  type  whose  principal 
features  are  incident  to  the  ways  in  which  the  forces  which  de- 
formed the  whole  region  acted  in  the  portion  of  the  region  oc- 
cupied by  it  at  different  phases  of  its  history  and  to  certain 
primary  variations  among  the  various  related  rocks  that  were 
laid  down  in  what  is  now  western  Vermont.  It  seems  probable 
that  distinctions  among  the  various  rocks  of  the  region  have  often 
been  made  on  secondary  features  and  that  an  essential  unity  in 
rock  type  and  structure  has  been  overlooked. 

A  tendency  to  regard  different  portions  of  the  region  as 
things  more  or  less  apart  has  appeared  in  one  form  or  other 
during  and  since  the  days  of  the  early  surveys,  and  it  may  be 
said  that  by  reason  of  the  heterogeneity  that  exists  over  western 
Vermont  as  a  whole,  on  account  of  primary  differences  among 
the  rocks  and  metamorphism  and  deformation,  it  is  not  surprising 
to  find  that  what  now  appear  to  be  subordinate  or  secondary 


272  REPORT  OF  the:  VERMONT  STATE  GEOLOGIST. 

features  have  been  emphasized  and  that  fundamental  similarities 
have  been  overlooked. 

In  the  first  place,  it  is  well  again  to  note  that  the  lake  with 
its  islands  differs  in  no  essential  way  from  the  mainland  areas 
which  adjoin  it;  the  clay  or  sand  or  bowlder  drift  that  usually 
conceals  the  hard  rock  on  the  mainland  differs  only  in  physical 
properties  from  the  water  of  the  lake.  In  fact,  as  has  already 
been  pointed  out,  in  many  places  near  the  lake  and  within  its 
confines,  clay  instead  of  water  may  be  said  to  inundate  the  land 
where  the  surface  of  the  hard  rock  is  below  the  present  water- 
level.  The  areas  of  the  hard  rock  now  beneath  the  waters  of  the 
lake,  or  beneath  the  deposits  of  one  kind  or  other  which  take 
their  place,  are  probably  primarily  old  stream  denuded  surfaces 
which  have  been  generally  modified  by  glacial  action  and  in  cer- 
tain portions  after  inundation  by  water  also  by  the  waves.  The 
topography  of  the  lake  region  stands  in  contrast  to  the  rest  of 
th^  Champlain  lowland  on  account  of  the  more  vulnerable  char- 
acter of  its  rocks,  whose  presence  at  the  surface  is  a  circum- 
stance consequent  upon  relations  produced  by  ancient  deforma- 
tions which  the  region  underwent. 

If,  as  seems  likely,  there  have  not  been  any  marked  displace- 
ments of  the  crust  during  or  since  the  action  of  the  erosive  agents 
which  shaped  the  present  surface,  then  the  several  physiographic 
divisions  of  the  region  may  be  regarded  as  chiefly  consequent 
upon  relations  produced  among  the  formations  by  crustal  dis- 
turbances. 

The  islands  of  the  lake  and  also,  without  much  doubt,  the 
hard  rock  surface  beneath  the  water,  as  well  as  extensive  areas  of 
the  adjacent  Vermont  mainland  over  which  the  hard  rock  is 
partly  exposed  and  partly  hidden,  are  dominated  by  rocks  which, 
although  altered  and  deformed  in  varying  degrees,  are  on  the 
whole  less  metamorphosed  and  less  crystalline  than  are  the  various 
formations  of  calcareous  rocks  found  over  the  areas  that  lie  to 
the  east  of  the  lake  region.  Away  from  the  lake  along  surface 
sections  from  west  to  east  at  some  latitudes  the  succession  is  often 
marked  by  a  sort  of  transition  from  comparatively  little  altered 
rocks,  through  others  in  which  fossils  have  been  largely  oblit- 
erated to  highly  metamorphosed  rocks  with  dim,  uncertain  traces 
or  else  no  suggestion  of  organic  remains.  Even  along  such  sec- 
tions it  should  be  understood  that  the  sequence  is  not  one  marked 
simply  by  difference  of  metamorphism  of  the  rock,  but  is  an  in- 
terrupted one  caused  partly  by  deformations  and  partly  by  ero- 
sion. In  some  sections,  on  account  of  displacements  and  thrusts 
which  have  moved  rocks  from  the  east  over  those  at  the  west,  the 
change  from  rocks  whose  geological  age  may  be  fairly  readily  ap- 
parent, at  least  so  far  as  the  fossils  are  understood,  to  rocks 
which  have  been  profoundly  altered  is  abrupt. 


REPORT  OF  THE  VERMONT   STATE  GEOLOiGIST.  273 

The  rocks  of  the  lake  region,  including  the  islands  and  much 
of  the  adjacent  mainland,  as  determined  by  their  fossils,  range  in 
age  from  lowest  Ordovician  (possibly  Upper  Cambrian),  "Ozark- 
ian,"  through  various  horizons  of  "Beekmantown."  Chazy  and 
Trenton,  possibly  to  horizons  that  are  homotaxial  with  the 
Utica  as  elsewhere  known.  The  so-called  Ozarkian  is  an  in- 
durated sandstone,  in  some  places  apparently  lying  conformably 
beneath  basal  Beekmanto%\Ti  magnesian  limestone.  In  Xew 
York,  in  the  Mohawk  valley  and  elsewhere,  these  two  formations 
are  described  as  separated  by  an  unconformity  which  it  is  claimed 
has  been  traced  into  the  Champlain  and  St.  Lawrence  valleys ;  but 
the  unconformit}-  in  the  lake  region  is  not  apparent  from  any 
physical  e^-idence.     The  fossils  are  scant\'  and  poorly  preserv-ed. 

The  East  Shoreham  section  appears  to  give  the  complete 
series  of  the  Beekmantown  of  the  lake  region,  but  elsev\-here 
usually  only  parts  of  this  formation  are  shown.  The  special 
characters  of  the  members  of  this  formation  will  not  be  described 
at  this  place.  "WTien  ail  are  present  the  thickness  has  been  esti- 
mated as  about  1.800  feet.  The  Chazy  succeeds  the  Beekman- 
town, and  at  some  places,  as  at  Isle  La  Motte.  the  lowest  beds  of 
the  series  show  indications  of  shallow  water  or  shore  origin,  sug- 
gesting oscillations  of  the  sea  bottom  and  probably  a  discon- 
formity.  In  a  large  number  of  places  the  Chazy  rocks  have  a 
considerable  thickness,  but  usually  this  formation,  like  the  Beek- 
mantown. is  apparently  only  partly  represented,  at  least  in  surface 
exposures.  At  numerous  localities  Chazy  rocks,  often  clearly 
belonging  to  the  intermediate  members  of  the  series,  or  so-called 
]\Iiddle  Chazy,  are  overlain  by  beds  of  dense,  "black  hmestone  of 
Black  River  age..  The  Black  River  is  suceeded  by  the  basal 
Trenton  (  "Glens  Falls'' j  limestone,  which  is  in  turn  followed  by 
a  series  of  argillaceous  limestones  and  shales,  some  of  which 
form  a  more  or  less  distinctly  transitional  group  with  respect  to 
both  litholog}^  and  fossils  between  the  basal  Trenton  limestone 
and  the  mud  rocks  that  make  up  the  youngest  Ordovician  of  the 
lake  region.  These  mud  rocks  are  apparently  of  Trenton  or  of 
Trenton-" L'tica""  age. 

Without  much  doubt,  the  original  primary  sequence  among 
the  various  rocks  now  exposed  to  view  in  the  immediate  region 
of  the  lake  was  as  above  given  and  may  be  summarized  as  follows : 

1.  "Ozarkian"  sandstone. 

2.  Beekmantown  siHceous  and  magnesian  limestones. 

3.  Chazy  limestone,  including  some  sandstone  at  the  base. 

4.  Black  River  limestone. 
Trenton  (basal  or  "Glens  Falls'")  Hmestone. 
Transitional  limestones  and  shales  ( "Canajoharie."'  Tren- 
ton, Ruedemann). 


274  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

7.  Later  shales  ("Stony  Point,"  Trenton,  Ruedemann), 
some  of  which  may  be  contemporaneous  with  Utica  as  elsewhere 
known  (New  York). 

Whether  the  different  formations  just  enumerated  are 
separated  from  one  another  or  are  broken  within  themselves  by 
erosion  intervals  will  not  be  discussed  at  len^h  in  this  paper. 
Apparently  our  present  knowledge  is  insufficient  to  decide  the 
matter  in  many  cases.  From  what  is  known  of  the  relations 
among  apparently  equivalent  formations  elsewhere,  as  in  New 
York  for  example,  disconformities  are  probably  present;  but  in 
Vermont  the  conditions  make  it  difficult  or  impossible  to  say 
whether  the  partial  representation  of  a  formation  at  many  places 
is  due  to  non-deposition  or  to  displacements  among  the  rocks.  At 
the  present  time  there  is  no  section  which  shows  all  these  forma- 
tions in  their  sequence.  In  some  places  a  surface  covering  un- 
doubtedly conceals  portions  of  formations ;  but  at  other  places 
parts  are  clearly  absent,  either  as  the  result  of  non-deposition  or 
from  other  causes. 

The  various  formations  of  the  lake  region  have  clearly  been 
disturbed  and  probably  by  more  than  one  deformation.  As  a 
whole  they  have  been  faulted  down  with  reference  to  the  crystal- 
line rocks  of  the  Adirondack  region ;  but  in  addition  they  show 
unmistakable  evidence  of  profound  compression  which  finds  ex- 
pression in  disturbed  relations  due  to  fracture  and  reverse  fault- 
ing within  the  various  formations  with  varying  degrees  of  actual 
overthrust,  which  sometimes  carried  the  older  rocks  on  the 
younger  limestones  and  shales.  The  less  resistant,  more  thinly- 
bedded  rocks  have  been  somewhat  broken  and  faulted  as  masses, 
but  have  been  more  conspicuously  sheared  by  fracture  cleavage ; 
the  more  massive  formations  were  also  internally  deformed  but 
were  more  characteristically  disturbed  by  mass  dislocation.  At 
some  places  it  is  very  evident  that  the  rocks  have  been  moved  and 
are  now  not  in  their  original  relations  to  other  rocks  with  which 
they  are  contiguous  and  at  other  places  the  presumption  is  often 
very  strong  that  displacements  have  occurred.  It  is  not  always 
easy  to  decide  whether  a  deformation  which  is  clearly  due  to 
compression  is  a  case  of  relatively  simple  reverse  faulting,  or 
whether  considerable  lateral  movement  with  actual  overthrust  has 
taken  place.  In  the  preceding  pages  the  probabilities  have  al- 
ready been  discussed  for  various  localities. 

In  the  lake  region  the  base  or  floor  on  which  the  series  of 
formations  above  enumerated  were  laid  down  is  not  exposed. 
One  would  suppose  that  at  some  depth  or  other  the  oldest  member 
of  the  lake  series  which  seems  to  be  the  so-called  Ozarkian  sand- 
stone must  rest  on  older  rock ;  but  rocks  older  than  this  sandstone 
which  apparently  could  have  formed  the  floor  of  the  Ozarkian 
sea  are  not  certainly  known  in  the  Vermont  portion  of  the  lake 
region,  except  the  members  of  the  Lower  Cambrian   formation 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  275 

which  have  been  brought  to  their  present  relative  positions  by 
thrust.  Furthermore,  the  Ozarkian  sandstone  at  no  place  where 
it  is  now  exposed  is,  so  far  as  the  writer  knows,  in  undisturbed 
condition,  but  on  the  contrary  occupies  its  present  position  by 
thrust.  On  the  west  side  of  the  lake  the  Potsdam  sandstone  is 
often  in  faulted  relations  with  the  members  of  the  lake  series. 
The  Lower  Cambrian  rocks  that  lie  to  the  east  of  the  lake  give 
only  a  vague  suggestion  of  what  is  at  depth  in  the  lake  region 
proper.  Presumably  these  Lower  Cambrian  rocks  extend  beneath 
the  lake  at  some  unknown  depth ;  but  what  immediately  overlies 
them  is  not  known. 

Why  the  various  thrusts  which  may  be  shown  to  exist  in  the 
immediate  lake  region  have  always  cut  through  the  Ozarkian  or 
some  younger  formation  it  is  not  easy  to  understand.  If  the  lake 
series  rests  on  older  rocks  than  the  Ozarkian  but  younger  than 
the  Lower  Cambrian,  one  wonders  why  such  rocks  do  not  now 
appear  at  the  surface  somewhere  br  other  in  the  lake  region.  The 
fact  that  they  do  not  and  that  the  members  of  the  Lower  Cam- 
brian do  not  appear  by  upthrust  west  of  their  present  margin 
forms  the  basis  of  the  conception,  first  clearly  formulated  by 
Logan,  that  there  was  a  great  lateral  thrust  fault  by  which  the 
older  masses  at  the  east  were  driven  over  the  rocks  of  the  lake 
region.  But  of  the  fact  that  the  members  of  the  lake  series  have 
themselves  in  varying  degrees  participated  in  thrust  movements 
there  is  now  no  longer  any  doubt. 

It  is  possible  that  there  exists  a  deep-seated  plane  of  major 
thrust  that  cut  through  the  roots  of  successive  reverse  faults  and 
that  this  plane  is  beneath  any  rocks  now  exposed  in  the  lake 
region  and  is  concealed  because  of  subsequent  normal  faulting 
which  dropped  all  the  rocks  that  lie  betweent  the  x\dirondack 
mass  and  the  Green  Mountain  plateau.  If  such  a  plane  exists  and 
if  it  cut  through  pre-Cambrian  rocks  it  might  not  be  easy  to  recog- 
nize and  could  hardly  be  detected  on  the  Vermont  side  of  the 
lake. 

On  the  New  York  side  of  the  lake  is  a  sandstone  of  Upper 
Cambrian  age  which  is  not  like  the  Ozarkian  sandstone  of  the 
lake  series  in  Vermont.  This  sandstone  has  not  been  recognized 
in  Vermont,  but  has  a  wide  distribution  on  the  east  and  north  of 
the  Adirondacks,  where  it  apparently  rests  unconformably  upon 
pre-Cambrian  rocks.  One  is  confronted  with  a  problem  of  great 
complexity  in  trying  to  account  for  the  deformations  and  primary 
conditions  which  could  have  produced  the  present  relations. 

It  seems  probable  that  so  far  as  thrusting  is  concerned  the 
situation  involves  some  such  history  as  follows :  Possibly  during 
a  time  when  overlying  masses  of  rock  which  are  now  eroded  were 
present  in  the  region,  there  occurred  more  or  less  extensive 
thrusts  by  which  older  formations  were  driven  through  younger 
ones.     These  great  shears,  as  such,  did  not  necessarily  pass  to  the 


276  REPORT  OF  THE  VERMONT  STATE  GEOLOGIST. 

surface  at  the  time  they  occurred,  although  if  they  did,  they 
seemingly  must  have  had  some  expression  there,  probably  as 
folds.  In  any  event  the  effect  obviously  was  to  bring  older 
against  younger  masses.  This  was  not  accomplished  in  any  set 
fashion,  but  by  irregular  displacements  of  varying  degrees.  There 
was,  however,  produced  a  considerable  regularity  in  the  relations 
which  certain  formations  came  to  have  to  one  another.  One 
may  imagine  that  at  certain  places,  notably  in  the  lake  region,  on 
account  of  diminishing  pressure,  older  rocks  were  not  driven 
into  overlying  formations  far  enough  to  cause  them  to  appear  at 
the  surface  during  later  erosion.  It  seems  also  probable  that 
during  such  deformation  older  rocks  were  often  carried  over 
relatively  unde formed  younger  formations  and  that  the  latter 
were  preserved  until  relatively  recent  times  by  a  covering  of  more 
resistant  rock.  The  present  preservation  of  relatively  soft  rock 
was  not  due,  however,  simply  to  the  service  of  a  protecting  cover- 
ing, but  was  favored  by  crustal  deformations  due  to  normal  fault- 
ing which  occurred  after  the  period  of  thrusting  and  which 
brought  different  areas  of  the  region  to  a  lower  elevation  with 
reference  to  the  base  level  of  erosion. 

It  seems  clear  that  all  the  different  rocks  were  subjected 
to  a  certain  amount  of  compression,  but  that  on  account 
of  the  massive  character  of  many  of  the  formations  in- 
volved, folding  was  subordinate  and  fracture  with  thrust  became 
the  dominant  type  of  displacement. 

There  are  .good  reasons  for  thinking  that  a  thrust  which  was 
initiated,  perhaps  as  a  reverse  fault,  in  one  formation  often 
sheared  away  from  it  into  an  overlying  one  and  that  from  such 
behavior  either  the  older  formation  or  the  one  overlying  it  was 
driven  over  a  still  younger  formation.  Various  modifications  might 
have  been  produced.  By  a  series  of  reverse  faults  preceding  the 
development  of  a  horizontal  thrust  the  latter  could  be  conceived 
as  cutting  the  planes  of  the  faults  at  depth  and  as  driving  several 
blocks  on  a  common  shear;  If  the  several  reverse  faults  were 
of  different  degrees  of  throw  the  thrust  might  have  cut  through 
younger  rock  at  the  west  than  at  the  east  or  have  driven  in  dif- 
ferent ways  at  dift'erent  places,  producing  final  effects  not  very 
different  from  those  resulting  from  the  mode  of  behavior  pos- 
tulated in  the  first  part  of  this  paragraph. 

The  applications  of  the  ideas  as  to  possible  or  probable  thrust 
behavior  which  have  just  been  given  depend,  however,  not  only 
upon  the  recognition  of  thrusting  as  the  dominant  mode  of 
deformation  of  the  region  under  compression  and  upon  the  present 
apparent  relations  which  the  various  formations  have  to  each 
other,  but  also  upon  the  relations  that  existed  among  these  forma- 
tions prior  to  the  action  of  pressure.  The  explanation  of  the  con- 
ditions which  now  exist  requires,  therefore,  some  examination  of 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  277 

the  question  of  the  probable  primary  relations  of  all  the  rocks  to 
each  other. 

For  the  lake  region  proper  the  probable, primary  sequence  of 
the  various  formations  now  found  within  it  has  been  given.  On 
the  New  York  side  of  Lake  Champlain,  for  the,  areas  that  lie 
along  or  at  various  distances  away  from  the  lake,  apparently 
studies  yet  remain  to  be  carried  out  in  detail  with  regard  to  ar- 
rangements among  the  rocks  with  special  reference  to  displace- 
ments. In  Vermont,  as  is  evident  from  the  descriptions  that  have 
been  given,  the  lake  rocks  have  been  disturbed  by  thrusts  and 
there  may  be  recognized  a  more  or  less  well  defined  zone  of  de- 
markation  at  the  present  surface  between  the  relatively  unaltered 
rocks  of  the  lake  region  and  others  lying  to  the  east  which  are 
either  visibly  more  altered  or  are  notably  different  in  age  and 
lithological  character.  This  zone  constitutes  what  has  long  been 
known  as  "Logan's  line." 

Regarding  this  zone  for  convenience  as  a  line,  by  which 
symbol  it  would  be  portrayed  on  a  map,  it  may  be  described  for 
purposes  of  summary  as  follows :  Entering  Vermont  from 
Canada  in  western  Highgate  it  follows  the  present  lake  shore  for 
two  or  three  miles,  then  extends  through  the  south-central  part 
of  Highgate  into  Swanton,  then  passes  approximately  through  the 
central  parts  of  Swanton  and  St.  Albans  to  St.  Albans  Bay. 
From  St.  Albans  Bay  southward  it  extends  roughly  parallel  with 
and  near  the  shore  in  the  southwestern  part  of  St.  Albans,  and  on 
through  Georgia  and  Milton  to  Colchester,  where  it  coincides 
with  the  present  shore  north  of  and  around  Malletts  Bay.  It 
cuts  across  Colchester  peninsula  to  the  shore  north  of  Burlington 
and  southward  across  Burlington  and  Shelburne  Bays.  From 
Shelburne  Bay  southward  across  the  southwestern  part  of  Shel- 
burne, on  through  Charlotte,  Ferrisburg,  Waltham,  the  south- 
eastern part  of  Addison,  and  the  northeastern  part  of  Bridport, 
the  surface  relations  usually  permit  fairly  definite  separation  of 
the  older  or  metamorphosed  rocks  from  the  lake  series,  but  drift 
often  more  extensively  separates  outcrops  and  hides  relations  in 
these  townships  and  from  Ferrisburg  to  Bridport  the  apparent 
line  of  separation  is  a  decidedly  sinuous  and  irregular  one  with 
encroachment  eastward  at  some  places  of  the  members  of  the 
lake  series  on  meridians  which  to  the  north  and  south  are  occupied 
by  overthrust  rocks. 

From  the  Canadian  boundary  to  Bridport  the  line  that  is  be- 
ing described  marks  for  the  most  part  an  abrupt  separation  of 
the  youngest  Ordovician  rocks,  which  are  generally  shales  with 
some  included  siliceous  bands,  from  more  or  less  altered  and 
metamorphosed  calcareous  rocks,  or  from  massive,  interbedded 
quartzites  and  dolomites  that  belong  to  the  Cambrian  system. 

From  northeastern  Bridport  southward  through  Shoreham 
into  the  northern  part  of  Orwell  the  Cambrian  rocks  are  concealed 


278  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

and  the  zone  of  overthrusting  is  occupied  by  not  very  greatly 
altered  rocks  belonging  to  the  Ozarkian  or  Beekmantown  forma- 
tions of  the  lake  series  which  take  the  place  of  the  members  of 
the  Red  Sandrock  formation  or  of  much  altered  calcareous  rock 
which  are  prominent  along  the  margin  of  overthrust  for  so  many 
miles  in  the  northern  townships.  In  the  latitude  of  Shoreham 
the  rocks  that  apparently  represent  the  Red  Sandrock  series 
farther  north  are  black  phyllites  with  interbedded  quartzite  mem- 
bers. These  rocks  lie  farther  east  in  Weybridge,  Cornwall  and 
Whiting  and  emerge  from  beneath  rnore  or  less  altered  calcareous 
rocks  that  may  in  some  cases  be  rather  satisfactorily  correlated 
with  members  of  the  lake  series.  The  phyllites  of  Whiting  join 
southward  with  those  of  Sudbury  at  the  northern  end  of  the 
Taconic  range.  The  phyllites  and  quartzites  of  Sudbury  and 
Hubbardton  pass  beneath  the  calcareous  rocks  of  eastern  Orwell 
and  northeastern  Benson,  which  are  of  Chazy-Trenton  age,  and 
rise  in  central  Orwell  and  in  Benson  to  form  high  hills  which  are 
on  meridians  occupied  by  the  Red  Sandrock  of  Snake  Mt.  in 
Addison  township. 

The  phyllites  and  quartzites  of  the  northern  part  of  the 
Taconic  range  are  here  and  there  overlain  b|y  Chazy  and  Trenton 
limestones  with  which  they  are  now  involved  through  thrusting 
and  faulting.  In  the  writer's  first  paper  an  attempt  was  made  to 
show  that  phyllites  and  quartzites,  like  those  of  the  Taconic  hills, 
probably  pass  beneath  the  various  calcareous  rocks  of  the  Ver- 
mont valley  and  join  with  similar  rocks  of  the  Green  Mountain 
plateau,  although  attention  was  distinctly  directed  to  the  prob- 
ability that  both  reverse  and  normal  fault  plane  now  separate  the 
rocks  of  the  Taconic  range  from  those  of  the  plateau. 

A  broad  acquaintance  with  the  rocks  of  western  Vermont 
would,  in  the  writer's  opinion,  serve  to  show  that  the  fractures 
and  displacements  constituting  the  zone  which  has  just  been  traced 
are  only  accentuated  instances  of  many  such  displacements  which 
break  the  rocks  along  their  strike  in  the  lake  region,  in  the  eastern 
parts  of  the  Champlain  lowland  and  along  the  western  margin  of 
the  plateau.  Along  Logan's  line,  so-called,  it  is  easier  to  discern 
the  presence  of  thrust  dislocations  because  of  the  wide  difiference 
in  age  and  lithological  characters  of  the  rocks  now  in  contact ;  in 
the  lake  region  and  particularly  in  the  areas  to  the  east  the  dif- 
ferences between  rocks  that  lie  in  displaced  relations  are  not 
always  so  readily  seen. 

The  rocks  east  of  Logan's  line  essentially  form  a  Cambrian 
surface.  Different  maps  that  have  been  published  and  different 
descriptions  of  the  region  have  recognized  the  presence  of  rocks 
of  later  age  than  the  Lower  Cambrian  here  and  there  over  this 
surface.  In  some  cases  the  rocks  that  with  more  or  less  definite- 
ness  may  be  distinguished  from  Lower  Cambrian  have  a  con- 
siderable extent  and  continuity,  but  on  the  whole,  they  may  be 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  279 

said  to  be  fragmentary  in  character,  as  now  preserved,  and  more 
or  less  intermingled  with  Lower  Cambrian  and  possibly  other 
Cambrian  rocks. 

The  rocks  which  in  this  paper  are  correlated  with  the  Lower 
Cambrian  are  far  from  being  homogeneous  throughout  their 
extent.  In  previous  pages,  frequent  mention  has  been  made  of 
the  manner  in  which  these  rocks  vary  in  lithological  character  in 
a  lateral  direction,  even  within  relatively  short  distances,  and 
vertically  from  bed  to  bed.  Some  types  of  rock  found  in  the 
terrane  have  a  wide  geographical  extent  in  the  region,  but  it  is 
not  certain  that  at  different  places  they  belong  to  the  same  horizons. 
Over  the  region  as  a  whole,  the  terrane  as  now  displayed  is  dis- 
tinguished by  notably  different  kinds  of  rocks,  some  of  which  are 
extensive  enough  to  be  regarded  as  formations ;  but  such  dif- 
ferences, even  though  pronounced,  seem  to  be  explainable  in  part 
as  due  to  differences  in  respect  to  sources  of  supply  of  material 
and  to  different  conditions  of  deposition  and  in  part  to  disturb- 
ances and  alteration  which  the  rocks  have  experienced.  Over  a 
large  part  of  the  region  an  ancient  Cambrian  surface  has  been 
partially  restored  by  processes  of  thrust;  it  is  not  a  perfect 
restoration,  partly  because  of  irregularity  of  thrust  and  partly 
because  of  erosion.  Within  the  areas  which  have  been  surveyed 
the  presumably  younger  rocks  that  are  here  and  there  intermin- 
gled with  the  Cambrian  in  the  lowland  have  not  been  found  on 
the  higher  land  that  borders  the  lowland  on  the  east. 

The  rocks  which  in  this  paper  are  correlated  with  Lower 
Cambrian  include : 

1.  Apparently  altered  derivatives  of  older  rocks  of  probably 
pre-Cambrian  age ;  sheared  quartzitic  rocks,  frequently  gneissoid 
or  coarsely  schistose,  sometimes  conglomeratic  and  sparingly 
arkosic,  found  at  numerous  places  along  the  western  marginal 
portion  of  the  Green  Mountain  plateau  and  in  the  hilly  land  ad- 
jacent to  it. 

2.  Extensive  areas  of  white  and  gray,  granular  quartzite, 
frequently  sheared  but  often  without  pronounced  internal  def- 
ormation, occurring  in  heavy  layers  or  as  thick  masses  of  rela- 
tively thin  beds.  These  rocks  grade  laterally  and  vertically  into 
flaggy  quartzites,  schists,  phyllites  and  slates.  These  various 
rocks  are  now  found  within  the  marginal  portions  of  the  plateau, 
and  along  the  eastern  portion  of  the  Champlain  lowland  and  mixed 
with  graywacke  quartzite  are  found  in  Weybridge,  Cornwall  and 
Whiting  and  in  the  northern  portion  of  the  Tacoriic  range. 

3.  Massive,  gray,  siliceous  dolomites  and  dolomitic  quartz- 
ites grading  laterally  into  one  another  and  into  quartzite  and 
downward  into  sheared  or  massive  quartzite  and  perhaps  laterally 
and  downward  into  schists  or  phyllites ;  grading  upward  and  per- 
haps laterally  into 

4.  More  or  less  distinctly  interbedded  dolomites  and  quartz- 
ites which  vary  in  different  parts  of  the  region  with  respect  to 
thickness  and  color  of  the  different  members. 


280  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

Members  of  3  are  common  along  the  margin  of  the  plateau 
and  ill  the  eastern  portion  of  the  lowland  in  association  with 
dififerent  members  of  2  and  with  different  phases  of  4  occur  over 
much  of  the  lowland,  intermingled  with  quartzite  or  schist,  or 
with  calcareous  rocks  of  probably  younger  age. 

These  different  rocks  appear  to  be  parts  of  the  same  general 
formation.  Ver}^  different  kinds  of  rocks  were  probably  essentially 
contemporaneous  and  all  together  probably  originally  composed  an 
essentially  conformable  series.  Published  descriptions  of  the  dif- 
ferent geographical  or  more  or  less  altered  phases  of  this  series 
have  differentiated  them  into  Granular  Quartz,  Talcoid  Slates 
and  Schists,  Talcoid  Conglomerate,  Dolomite,  Red  Sandrock.  etc. 
and  have  recognized  only  in  part  what  the  writer  believes  to  be 
their  essential  contemporaneity.  Into  the  nomenclature  that  has 
at  one  time  or  other  been  employed  to  describe  these  rocks  there 
have  crept  some  terms  indicative  of  age  which  seem  to  be  in  many 
cases  distinctly  misleading  in  their  implication. 

Topographic  conditions-may  be  largely  discounted.  Present 
geological  relations  must  reckon  with  the  evidence  that  the  rocks 
of  western  Vermont  have  been  jammed,  sheared,  faulted  and 
driven  over  one  another.  Ancient  effects  due  to  compression  and 
normal  displacements  which  apparently  came  later  are  sufficient 
to  account  for  most  of  the  field  relations,  if  the  principle  of 
lateral  variation,  as  discussed  in  preceding  pages,  be  allowed. 

Fossils  have  been  found  by  different  workers  at  various 
places  in  western  Vermont  among  the  rocks  enumerated  above  and 
correlated  with  the  Cambrian.  Most  of  the  fossils  are  regarded 
as  of  Lower  Cambrian  age. 

Some  observers  have  assigned  a  different  and  much  later  age 
to  certain  rocks  which  have  not  yielded  fossils  and  which  the 
writer  regards  as  probably  parts  of  the  Lower  Cambrian.  Such 
assignment  has  apparently  often  been  based  on  such  features  as 
superposition  with  respect  to  rocks  probably  younger  than  Lower 
Cambrian  and  intimate  field  association  with  such  rocks.  Such 
relations  might  readily  have  been  produced  by  thrusts  and  other 
displacements,  as  has  been  elsewhere  discussed. 

Others  have  "hazarded"  an  opinion  that  at  some  places  some 
members  of  the  series  that  is  herein  regarded  as  probably  Lower 
Cambrian  may  be  of  Middle  Cambrian  age ;  but  apparently  such 
opinion  is  based  on  the  idea  that  the  thickness  which  has  been 
assigned  to  the  Lower  Cambrian  is  too  great  along  certain  sec- 
tions in  which  the  rocks  appear  to  be  conformable.  Again  it 
seems  that  sufficient  account  has  not  been  taken  of  the  deforma- 
tions of  the  region  and  the  probable  existence  of  displacements  in 
an  apparently  conformable  series. 

It  is  recognized  that  fossils  have  been  found,  as  has  been 
mentioned  in  this  paper,  which  suggest  a  Middle  or  late  Cam- 
brian age   for  certain  rocks   now  present  in   western   Vermont. 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  281 

The  localities  at  which  these  fossils  were  found  are  in  the  north- 
western part  of  the  State.  The  rocks  yielding  them  are  in  some 
places  slates,  in  others,  a  peculiarly  fragmental  rock  which  has 
been  referred  to  as  an  "intraformational  conglomerate." 

From  the  time  when  the  Cambrian  rocks  of  western  Ver- 
mont, which  were  first  called  Middle  Cambrian,  were  recognized 
as  belonging  to  the  lower  part  of  the  Cambrian  system  it  has 
usually  been  supposed  because  of  failure  to  discover  over  any 
considerable  portion  of  the  region,  fossils  that  could  positively  be 
called  Middle  or  Upper  Cambrian,  that  rocks  belonging  to  those 
horizons  were  never  deposited  in  what  is  now  western  Vermont. 
It  cannot  be  affirmed  to-day  that  such  rocks  were  ever  laid  down 
over  any  considerable  part  of  it.  But  taking  such  fossils  as  have 
been  found  at  their  face  values,  it  would  appear  that  Cambrian 
j-ocks  later  than  the  Lower  Cambrian  were  formed  in  some  parts 
of  the  region. 

It  apparently  does  not  follow  from  failure  to  find  Middle  or 
later  Cambrian  rocks  preserved  over  the  region  as  a  whole,  that 
such  were  never  present.  It  is  clearly  necessary  to  recognize 
that  such  rocks  may  have  been  eroded.  But  if  such  rocks  were 
ever  present  and  were  later  eroded  it  is  reasonably  clear  from 
present  field  relations  that  they  were  removed,  at  least  for  the 
most  part,  prior  to  the  deposition  of  th^various  calcareous  rocks 
of  presumably  later  date  that  are  now  intermingled  with  rocks 
that  apparently  belong  to  the  Lower  Cambrian. 

The  present  conditions  in  western  Vermont  seem  to  point  to 
some  sort  of  disturbance  of  the  region  after  the  Lower  Cambrian 
rocks  were  laid  down.  This  disturbance  may  have  occurred  so 
early  in  the  Cambrian  that  late  Cambrian  rocks  were  formed  only 
in  a  small  part  of  the  region  or  it  may  have  occurred  after  Cam- 
brian rocks  younger  than  the  Lower  Cambrian  were  widely  dis- 
tributed. There  seems  to  be  no  positive  evidence  to  show  which 
condition  was  more  probable.  The  apparent  result  was  a  de- 
nuded Cambrian  surface  which,  except  as  it  has  been  more  or 
less  deformed  and  eroded  subsequent  to  deformation,  is  what 
we  see  to-day.  This  eroded  surface  was  submerged  and  on  it  were 
laid  down  rocks  of  younger  age  than  the  Cambrian. 

On  account  of  the  profound  deformation  of  the  whole  region 
after  these  later  rocks  were  deposited,  their  original  relations  to 
the  denuded  surface  on  which  they  were  laid  down  are  everywhere 
greatly  obscured.  At  no  place  which  the  writer  has  visited  can 
there  be  clearly  identified  at  the  present  time  an  unconformable 
sedimentary  contact  between  the  Cambrian  and  younger  rocks, 
while  at  the  same  time,  apparently  little  doubt  may  be  entertained 
that  most  of  the  altered,  calcareous  rocks,  with  some  of  which  the 
members  of  the  Cambrian  are  now  associated  or  even  contiguous, 
are  younger  than  the  latter  and  separated  from  them  by  a  great 
unconformity.     This  seems  to  be  the  situation  practically  every- 


282  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

where,  both  in  the  lowland  regions  and  in  parts  of  the  Taconic 
range.  It  is  conceivable  that  in  some  parts  of  the  region  late 
Cambrian  rocks  were  not  completely  eroded  before  the  denuded 
Cambrian  land  mass  was  submerged ;  but  if  such  is  the  case  the 
localities  are  apparently  few  in  number. 

Where  later  Cambrian  rocks  remained  in  place  after  general 
denudation,  it  is  not  difficult  to  imagine  that  when  these  rocks 
were  washed  by  a  transgressing  sea  fossils  of  Middle  and  pos- 
sibly Upper  Cambrian  age  could  have  been  involved  and  pre- 
served in  the  basal  member  of  a  transgressing  series,  which  mem- 
ber instead  of  being  of  Cambrian  age  would  belong  to  a  much 
later  date.  Cambrian  types  might  or  might  not  have  been  inter- 
mingled with  other  fossils. 

The  so-called  "intraformational  conglomerate"  from  its  field 
relations  often  appears  to  be  a  facies  of  the  basal  member  of  a . 
younger  formation  that  was  deposited  on  an  eroded  Cambrian 
surface.  It  was  hoped  that  in  Vermont,  fossils  might  be  found 
in  the  matrix  of  the  conglomerate  that  would  confirm  this  idea ; 
but  up  to  the  present  time  the  writer  has  found  nothing  that  is 
conclusive. 

The  conglomerate  formation  in  its  Georgia  occurrence  was 
described  by  Walcott  as  a  great  lenticle  or  lentile  in  the  Cambrian 
series ;  its  present  distribution  and  relations  in  some  places  do  not 
seem  to  bear  out  this  idea. 

The  conglomerate-  may  be  traced  from  its  outcrops  in  High- 
gate  southward  through  S wanton  and  St.  Albans  into  Georgia, 
but  it  occurs  as  detached  areas  and  very  apparently  as  a  facies  of 
a  formation  which  includes  some  calcareous  sandstone,  thinly- 
bedded,  blue  limestones  and  shaly  rocks.  The  conglomerate  is 
sometimes  only  slightly  developed  as  a  lateral  variation  of  lime- 
stone beds  and  then  is  usually  fine  grained.  In  other  places  it 
is  more  extensive  and  composed  of  bowlders  of  all  sizes,  usually 
with  a  matrix  of  calcareo-siliceous  material  and  arenaceous  tex- 
ture. The  formation  is  from  all  appearances  represented  at  some 
places  in  the  northern  townships  by  bluish  limestones  in  which 
the  conglomeratic  phase  in  present  exposures  is  either  not  at  all 
or  only  sparingly  present.  South  of  Georgia,  in  Milton  and  Col- 
chester, rocks  which  in  a  more  or  less  satisfactory  way  may  be 
correlated  with  this  formation  are  only  sparingly  present  in  sur- 
face exposures.  These  have  been  mentioned  in  preceding  pages. 
In  Williston  township  near  Brownell  Mt.  and  west  of  it,  thinly- 
bedded,  bluish  limestones  were  noted ;  but  south  of  the  Winooski 
River  the  calcareous  rocks  which  are  intermingled  in  surface 
outcrops  with  quartzite,  dolomite,  or  interbedded  quartzite  and 
dolomite  are  striped,  blue  limestones  and  bluish  or  white,  marbly 
rocks  in  which  conglomerate  was  not  noted. 

The  usually  distinctly  crystalline  and  often  highly  metamor- 
phosed, calcareous  rocks  that  are  intermingled  with  the  Cambrian 


REPORT  OF  THE  VERMONT  STATE  GEOLOGIST.  283 

beds  over  the  lowland  region  south  of  the  Winooski  River  and 
east  of  the  western,  marginal  zone  of  overthrust  of  Cambrian 
and  other  rocks  on  the  lake  series  have  been  mentioned  somewhat 
in  detail  in  preceding  pages.  Attention  was  frequently  directed 
to  the  resemblance  which  many  of  these  rocks  have  to  members 
of  the  lake  series.  These  rocks  have  not  often  yielded  fossils. 
In  a  few  cases  they  have  afforded  obscure  or  recognizable  mark- 
ings of  shells  of  gastropods  or  cephalopods  on  the  basis  of  which 
they  have  been  called  Beekmantown,  Chazy  and  Trenton. 

Published  descriptions  and  maps  of  the  eastern  portion  of 
the  lowland  south  of  the  Winooski  River  have  certainly  confused 
Cambrian  rocks  with  others.  On  account  of  the  confusion  which 
exists  it  would  not  be  easy  to  distinguish  the  various  rocks  from 
one  another  on  a  map.  It  does  not  seem  surprising  that  Hitch- 
cock was  puzzled  by  these  rocks  and  that  in  the  absence  of  any 
means  of  separating  them  he  embraced  them  all  in  one  formation 
called  the  "Eolian  Limestone."  Later  observers  have  apparently 
done  what  amounts  to  the  same  thing. 

Since  Hitchcock's  time  some  progress  has  been  made  in 
separating  the  members  of  his  Eolian  Limestone  on  the  basis  of 
fossils ;  but  apparently  if  we  are  to  understand  the  geology  of  the 
areas  of  disturbed  and  altered  rocks  of  the  eastern  part  of  the 
lowland,  the  Vermont  valley  and  the  Taconic  range,  other  criteria 
will  have  to  be  used^  as  well  as  fossils. 

In  the  work  of  finding  the  fossils,  Mr.  Wing  wrought  with 
great  perseverance.  Proceeding  east  from  the  lake  region  he 
"identified"  the  Trenton  east  of  the  "central  belt  of  slate"  in 
Leicester,  Cornwall  and  Middlebury.  He  found  the  Chazy  at 
West  Rutland,  and  Trenton  rocks  in  the  northern  hills  of  the 
Taconic  range.  The  Chazy  was  described  as  affording  fossils  in 
Leicester,  Cornwall  and  Middlebury,  while  by,  means  of  the 
"striped  stratum"  the  Chazy  was  traced  into  the  western  part  of 
Brandon,  in  the  fields  and  quarries  of  that  town,  and  from  Bran- 
don southward  into  Pittsford  and  northward  into  Salisbury. 
Beekmantown  (Calciferous)  beds  were  also  described  as  occur- 
ring in  Salisbury,  Leicester  and  Brandon  with  their  fossils. 

In  a  section  reproduced  by  Dana^  from  Wing's  notes  and 
intended  to  show  the  arrangement  of  the  rocks  from  west  to  east, 
beginning  with  the  Red  Sandrock  in  eastern  Shoreham  and  ex- 
tending to  the  quartzite  east  of  the  main  belt  of  "Eohan  Lime- 
stone" in  Leicester,  beds  are  shown  as  Lower  and  Upper  Cal- 
ciferous which  probably  are  interbedded  dolomites  and  quartzites 
belonging  to  the  Lower  Cambrian. 

From  the  investigations  of  Wing  and  from  the  writer's 
studies,  it  appears  that  Chazy  and  Trenton  rocks  are  present  in 
the  main  belt  of  the  "Eolian  Limestone."  The  Beekmantown 
may  be  present  in  the  western  part  of  this  belt,  but  the  data  are 

lAmer.  Jour.  Sci.,  Vol.  XIII,  May,  1877. 


284  REPORT  OP  THE  VERMONT  STATE  GEOLOGIST. 

not  C(?nclusive.     Some  of   the   rock  so  described   appears  to  be 
Chazy  and  some  of  it  is  Cambrian. 

From  the  evidence  that  has  come  in  of  various  kinds,  it  now 
appears  that  a  broad  region  of  denuded  Cambrian  rocks  was 
gradually  submerged  in  Ordovician  time  and  was  transgressed  hf 
an  Ordovician  sea.  The  overlap  probably  began  at  the  west,  but 
from  present  field  relations  it  is  not  clear  just  how  the  transgres- 
sion proceeded.  The  altered  calcareous  rocks  now  distributed 
among  the  Cambrian  rocks  over  the  eastern  portion  of  the  Cham- 
plain  lowland  and  the  Vermont  valley  and  parts  of  the  Taconic 
range  are  probably  largely  the  eastern  representatives  of  members 
of  the  lake  series.  By  faulting  and  thrusting  the  younger  rocks 
have  been  much  disturbed,  together  with  the  Cambrian  floor  on 
which  they  originally  lay.  The  Cambrian  beds  have  in  many 
places  been  thrust  into,  through  and  over  the  younger  limestones. 
In  the  process  the  latter  have  been  sheared  and  metamorphosed  so 
that  they  can  be  with  difficulty  identified  with  their  representatives 
farther  west  near  the  lake. 

The  character  of  the  basin  in  which  these  younger  rocks  were 
deposited  is  not  now  clear.  It  seems  probable  that  there  was  in 
general  a  sort  of  trough  produced  by  a  warping  of  the  crust  and 
that  there  occurred  a  sort  of  periodic  pivotal  oscillation  of  land 
and  sea  bottom,  producing  retreat  and  advance  of  the  strand  line. 
One  of  these  seems  to  have  occurred  at  the  close  of  the  Middle 
division  of  the  Chazy  and  another  at  the  close  of  the  Upper 
Chazy.  Similar  episodes  may  have  occurred  during  the  Cam- 
brian. The  older  parts  of  the  trough  were,  however,  gradually 
deepened  and  the  positive  areas  were  slowly  submerged.  The 
Beekmantown  apparently  never  reached  far  to  the  east,  but  part 
of  the  Chazy  encroached  eastward  as  the  trough  widened.  A 
positive  movement  confined  the  Upper  Chazy  to  the  present  lake 
region,  but  a  resubmergence  brought  in  the  Black  River  and  Tren- 
ton. Whether  the  later  mud  rocks  ever  lay  over  the  disturbed 
areas  east  of  the  lake  it  is  hard  to  tell.  How  far  east  the  lake 
rocks  may  once  have  extended  may  only  be  conjectured. 

There  are  reasons  for  thinking  that  the  Cambrian  rocks  and 
the  younger  rocks  involved  with  them  have  in  general  moved 
as  a  whole  for  a  considerable  but  indeterminate  distance  west- 
ward over  the  eastward  extension  of  the  lake  rocks.  In  Ferris- 
burg,  along  Lewis  Creek,  the  Ordovician  shales  extend  a  con- 
siderable distance  to  the  east  of  the  irregular  margin  of  thrust 
overlap  of  older  rocks.  These  shales  appear  to  be  on  the  under 
side  of  a  great  lateral  thrust.  At  numerous  places  along  the 
present  shore  of  the  lake  members  of  the  Lower  Cambrian  or 
limestones  clearly  older  than  the  shales  lie  on  the  latter  by  thrust. 
At  some  places  also  there  are  indications  of  remnants  of 
overthrust  rocks  isolated  among  the  shales  and  now  some  distance 
removed  from  the  apparently  recessional  margin  of  older  rocks 


REPORT  OP  THE  VERMONT  STATE  GEOLOGIST.  285 

lying  to  the  east  of  them.  It  seems  possible  that  isolated  patches 
of  quartzite  found  among  the  shales  in  the  flat  land  in  the  western 
part  of  St.  Albans  township  may  be  such  remnants.  The  thought 
occurred  that  these  outcrops  might  be  exposures  of  older  rocks 
that  had  been  thrust  through  the  shales,  but  such  history  seems 
unlikely.  That  the  quartzite  belongs  to  a  different  formation 
from  the  shales  is  apparent,  for  no  such  rock  has  anywhere  been 
found  making  up  a  part  of  the  shale  formation. 

In  Orwell  there  are  detached  masses  of  massive  Beekman- 
town  limestone  which  are  apparently  surrounded  by  shale  and 
which  may  be  thrust-erosion  inliers  of  older  rock. 

SUPPLEMENTARY  NOTE. 

During  the  summer  of  1923  the  ledge  in  the  bank  of  Rock  River, 
at  the  bridge  near  Johnson's  farm,  was  revisited.  A  number  of  addi- 
tional fossils  were  found,  among  which  were  well  preserved  valves  of 
Nisusia  {OrtMsina)  festinata  {Billings)  and  the  pygidia  of  Eodiseus 
(Microdiscus)  speciosus  (Ford).  These  fossils  were  sent  to  Dr.  Ruede- 
mann  of  Albany  for  his  inspection.  Dr.  Ruedemann  confirmed  the 
writer's  recognition  of  the  trilobite  and  identified  the  brachiopod. 

The  ledge  in  which  these  fossil  fragments  were  found  is  just  north 
of  the  west  end  of  the  bridge.  The  outcrop  yielding  fossils  is  small 
and  partly  covered  with  soil,  but  the  rock  seemed  to  be  in  place.  In 
lithology  it  is  not  just  like  the  banded  limestone  that  lies  in  the  bank 
just  beneath  and  which  forms  the  bed  of  the  stream  above  and  below 
the  bridge. 

The  fossils  are  clearly  of  Lower  Cambrian  age;  but  it  is  not  cer- 
tain that  all  the  limestone  associated  with  the  rock  carrying  the  fossils 
is  of  similar  age. 


nmu  ¥39JQ38  z?.m  %  m 


PROGRESS  OF  STREAM  GAGING  IN  VERMONT 

During  the  Two- Year  Period  Ending  September  30,  1922. 


C.  H.  Pierce. 


DEPARTMENT  OF  THE  INTERIOR, 
UNITED   STATES   GEOLOGICAL   SURVEY. 


WATER   RESOURCES   BRANCH 

Boston,  Novemer  20,  1922. 
To  THE  Honorable,  The  Governor  of  Vermont, 

State  House,  Montpelier,  Vt. 
Dear  Sir: 

During  the  biennial  period  of  1921-1922,  the  investigation  of 
water  resources  of  Vermont  has  been  carried  on  by  the  United 
States  Geological  Survey  in  cooperation  with  the  State  of  Ver- 
mont, the  cooperating  state  official  being  Mr.  H.  M.  Mcintosh, 
State  Engineer,  during  1921,  and  Mr.  George  A.  Reed,  State 
Engineer,  during  1922. 

The  work '  of  measuring  the  flow  of  the  rivers  has  been 
continued  during  these  two  years,  and  the  results  of  stream  gaging 
at  ten  stations  are  shown  by  the  accompanying  tables.  Efforts 
have  been  made  to  continue  the  records  throughout  the  winter 
periods,  and  this  has  been  very  successful,  despite  the  fact  that 
very  low  temperatures  are  experienced  at  times.  The  mainte- 
nance of  the  gaging  stations  during  the  winter  and  the  making 
of  measurements  under  ice  conditions  are  much  more  difificult 
and  expensive  than  the  maintenance  during  the  summer  months, 
but  inasmuch  as  the  lowest  stages  of  the  rivers  in  Vermont  are  as 
likely  to  occur  during  February  as  any  other  month  of  the  year, 
it  seems  very  essential  to  obtain  information  of  the  flow  during 
the  winter  periods. 

In  addition  to  the  work  of  maintaining  gaging  stations  men- 
tioned above,  we  have  also  made  a  tabulation  of  the  existing  water 
power  developments  and  notes  as  to  where  additional  power  could 
be  obtained.  Although  the  most  obvious  power  sites  have  al- 
ready been  put  into  use,  there  still  remain  many  opportunities  for 
additional  power  development.  With  the  increasing  difficulties 
in  obtaining  fuel  for  steam  power,  it  is  apparent  that  more  difficult 
and  expensive  water  power  development  will  be  made  use  of  in 
the  near  future.  A  study  of  the  stream  flow  records  will  show 
that  a  very  large  percentage  of  the  total  run-ofif  from  the  rivers 
goes  to  waste  during  the  spring  months  and  at  other  times  when 


IINIV.  OF  NASI  GEOLOfiy  UBRARY 


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